Exposure apparatus and a method for exposing a photosensitive element and a method for preparing a printing form from the photosensitive element

ABSTRACT

The invention pertains to an exposure apparatus, a method for exposing a photosensitive element to radiation using the exposure apparatus, and a method for preparing a printing form from the photosensitive element. The exposure apparatus includes a base assembly having an exposure bed that supports the photosensitive element, and a lamp housing assembly having one or more lamps. The base assembly includes an assembly for controlling the temperature of the exposure bed to heat and cool the bed; and an assembly configured to remove air between the photosensitive element and an exterior top surface of the exposure bed.

BACKGROUND OF THE INVENTION

1. Field of the Disclosure

This invention pertains to an apparatus and method for preparing aprinting plate from a photosensitive element and, in particular, to anapparatus and method for exposing the printing form to actinicradiation.

2. Description of Related Art

Flexographic printing plates are well known for use in relief printingon a variety of substrates such as paper, corrugated board, films, foilsand laminates. Flexographic printing plates can be prepared fromphotosensitive elements containing a layer of a photosensitivecomposition such as those described in U.S. Pat. Nos. 4,323,637 and4,427,759. Photosensitive compositions, which may be referred to asphotopolymerizable compositions, generally contain an elastomericbinder, at least one monomer, and a photoinitiator. Photosensitiveelements generally have the layer of the photopolymerizable compositioninterposed between a support and a cover sheet or multilayer coverelement. Upon imagewise exposure of the photosensitive element toactinic radiation, photopolymerization of the photosensitive compositionoccurs in the exposed areas, thereby curing and rendering insoluble theexposed areas of the layer. The exposed element can be treated with asuitable solution or treated thermally to remove areas of thephotopolymerizable layer that were not exposed which provides a printingrelief suitable for use in flexographic printing.

Most commercial flat-bed exposure apparatuses include at least one bankof tubular lamps, which is formed from a plurality of light tubes thatare arrayed to form a wall-like effect. The tubular lights are typicallyfluorescent lamps that emit ultraviolet radiation at or in the range ofwavelengths necessary to cause photochemical reaction of the exposedportions of the photosensitive element. A plurality of light tubes isnecessary in order to achieve the actinic radiation energy necessary forphotopolymerization of the photosensitive element to occur. Some othercommercial flat-bed exposure apparatuses include two banks of tubularlamps. At least for exposure of the photosensitive element, the twobanks of light tubes are spaced apart, opposite and parallel the other,and the element which is supported on a glass bed is located between thebanks. In some cases, the position of one or both banks of tubes may beadjusted to create an appropriate space between the banks to accommodateexposing photosensitive elements. In other cases, an upper bank of lighttubes is used for imagewise exposure and/or back exposure of thephotosensitive element; and, a lower bank of light tubes is used forlight-finishing exposure and post exposure of the relief formed printingplate through the glass bed. In some instances the light-finishing andpost exposures are conducted as one step.

In most commercial flat-bed exposure apparatuses the photosensitiveelement is supported on the glass bed that is surrounded by ports, whichin combination with a transparent membrane or coversheet that covers thephotosensitive element and a negative film or phototool, draws a vacuumto bring the negative film in intimate contact with the photosensitiveelement prior to imagewise exposure. Imagewise exposure through anegative film or phototool having image-bearing art-work that is held inintimate contact under vacuum to the photopolymerizable layer of thephotosensitive element is often referred to as analog workflow. Analogworkflow requires the preparation of the phototool, which iscomplicated, costly and time-consuming process requiring separateprocessing equipment and chemical development solutions. In addition,the phototool may change slightly in dimension due to changes intemperature and humidity, and when used at different times or indifferent environments, may give different results, which can ultimatelyresult in the mis-registration of multicolor images during printing. Useof a phototool also requires special care and handling when fabricatingflexographic printing forms to ensure intimate contact is maintainedbetween the phototool and photosensitive element. In particular, care isrequired in the placement of both the phototool and the photosensitiveelement in the exposure apparatus along with special materials, e.g.,bleeder strips, to minimize air entrapment during creation of a vacuumto ensure intimate contact. Additionally care must be taken to ensureall surfaces of the photosensitive element, the phototool, and thetransparent membrane, are clean and free of dust and dirt. Presence ofsuch foreign matter can cause lack of intimate contact between thephototool and the photosensitive element as well as image artifacts.

Alternatively, imagewise exposure can be through an in-situ mask havingradiation opaque areas and transparent areas that had been previouslyformed above the photopolymerizable layer, so called digital workflow.In most instances of digital workflow, the in-situ mask is formed from aradiation-opaque layer that is integral with the photosensitive element,and thus there is no need to draw vacuum to assure contact of thein-situ mask with the element prior to imagewise exposure. Thephotosensitive element can be imagewise exposed in the presence ofatmospheric oxygen for conventional digital workflow as described inU.S. Pat. No. 5,262,275; U.S. Pat. No. 5,719,009; U.S. Pat. No.5,607,814; U.S. Pat. No. 6,238,837; U.S. Pat. No. 6,558,876; U.S. Pat.No. 6,929,898; U.S. Pat. No. 6,673,509; U.S. Pat. No. 6,037,102; andU.S. Pat. No. 6,284,431. Alternatively, the photosensitive element canbe imagewise exposed in an environment having an inert gas and acontrolled amount of oxygen that is less than atmospheric oxygen formodified digital workflow, by placing the photosensitive element in anexposure enclosure or chamber of an exposure apparatus as described, forexample, in U.S. Pat. No. 8,241,835. In one embodiment, the enclosurecan be sealed from external environment (room conditions) and includesan inlet port for introducing the inert gas and optionally additionaloxygen into the enclosure and an outlet port for purging the air that isinitially in the enclosure. The conventional digital workflow and themodified digital workflow each provide particular relief structure inthe resulting printing form that has specific characteristics andqualities to print desired quality images and graphic information forcertain end-use applications. Another digital workflow method disclosedby Zwadlo in U.S. Pat. No. 7,279,254, includes forming a mask digitallyin a thermal imaging layer of a separate film, laminating the film withthe mask to the photosensitive element, and imagewise exposing thephotosensitive element through the laminated mask film. As such, digitalworkflow because of its ease of use and desirable print performance hasgained wide acceptance as a desired method by which to produce aflexographic printing form from the photosensitive element.

However with ever increasing demands on quality, the currentstate-of-the-art flexographic printing forms may not perform as desiredand have trouble meeting the ever increasing demands on quality.Exposure times vary from a few seconds to a several minutes dependingupon the output of the lamps, distance from the lamps, desired reliefdepth, and the thickness of the photosensitive element. Since thephotosensitive element is exposed to actinic radiation at threedifferent steps in its conversion to a relief printing form, whichincludes a back exposure through the support, and imagewise exposurethrough the mask, and a post-exposure and finishing exposure, it isparticularly desirable to create and maintain uniform conditions in theexposure apparatus so that the photosensitive element experiencesconsistent environment and uniform distribution of actinic radiationduring each of these exposures. If the actinic radiation energyimpinging the photosensitive element is too low, polymerization reactionmay not start at all or may not occur deep enough in the layer of thephotosensitive material which impacts the shape of small raised printingelements of the relief image. If the actinic radiation energy impingingthe photosensitive element is too high such that the exposure timebecomes very short, the shape of the raised printing elements is alsopoor. The raised printing elements have a shoulder, which is a portionof the raised printing element that transitions from a flat printingarea to a sidewall, which becomes too steep, and small dots or lines donot have sufficient base and can easily chip away during printing.

Typically exposure apparatuses include a plurality of lamp tubes inorder to achieve the actinic radiation energy necessary forphotopolymerization of the photosensitive element to occur. Duringexposure the plurality of lamps is often in very close proximity to thephotosensitive precursor. Due to the number and proximity of the lampsto the photosensitive element, and duration of the exposure, thetemperature of the photosensitive element during exposure can change,i.e., increase, during exposure. It is also desirable to maintain thetemperature constant on the photosensitive element, and avoid relativelyhot or cool regions of the photosensitive element. Temperature changesof the photosensitive element, particularly during imagewise exposure,can influence the effect of oxygen inhibition and the rate of thephotochemical reaction/s that occur, and therefore can impact theformation of raised features, particularly the fine highlight dots, ofthe relief structure of the resulting printing form. A photosensitiveelement is exposed in many prior art exposure apparatuses in which theprecursor is at an ambient temperature at the start and the precursor isat a temperature above ambient at the end of the exposure. Some exposureapparatuses counter the possible temperature increase of thephotosensitive element by cooling the exposure bed on which thephotosensitive element rests. Some examples of commercial flat-bedexposure devices having an exposure bed that is cooled are CYREL®1000ECLF, 1000ECDLF, DF1000ECLF, and DF2000EC sold by DuPont(Wilmington, Del., USA); Concept 302ec, 302eclf, 302ecdlf, 305edlf,400ec, 400eclf, and 501 ec sold by Glunz & Jensen (Ringsted, Denmark);and, Nyloflex Next Exposure FII, Next Exposure FV, Exposure unit FIII,Exposure unit FIV, Exposure unit FV, and Combi Fill sold by Flint(Luxembourg, Luxembourg). But even with the photosensitive elementsupported on a cooled exposure bed, the photosensitive element willstill experience temperature changes during exposure. At the start ofexposure the bed will be cool and the plurality of lamps will not havehad sufficient time to warm the photosensitive element; and as theexposure progresses, the lamps will warm the photosensitive element butthe cooled bed will mitigate significant increase in the temperature ofthe photosensitive element.

Problems can also arise with the quality and uniformity of the radiationemitting from each of the lamps and thus impinging the photosensitiveelement for a single exposure, as well as for one exposure of aphotosensitive element to another exposure of a different photosensitiveelement, i.e., for exposures of multiple photosensitive elements over aperiod of time, particularly over the lifetime of the lamps. Duringexposure, the radiation impinging the photosensitive element should beevenly distributed over the area of the exposure bed, so that the entireexposed surface of the photosensitive element is uniformly irradiated.The plurality of light tubes when energized typically generates heat,which particularly in an enclosed environment interior to the exposureapparatus can influence the temperature of the lamps. So much heat maybe generated by the lamps that the lamps overheat, and it can becomedifficult to maintain the lamps at a constant temperature or within adesired temperature range. It is desirable to maintain the temperatureconstant from lamp to lamp within the plurality of light tubes, as wellas along the axial length of each of the lamps, and avoid relatively hotor cool regions in the lamps and from lamp to lamp. Barral et al. inU.S. Pat. No. 5,983,800 describe a machine for insolating photopolymerplates to ultraviolet light that delivers a flow of cooling air to themachine top in the vicinity of a negative, the photopolymer plate and atransparent membrane used to draw vacuum; and includes a bank of fans orblowers to provide some cooling of the bank of ultraviolet lamps.However, not all lamps of the bank of lamps are equally cooled by merelyblowing air across the lamps to cool the lamps since relatively hot orcool regions can occur in the lamps and from lamp to lamp. Non-uniformlamp temperatures will generate non-uniformity in the irradiance of theradiation emitting from the lamps and thus impinging the photosensitiveelement.

Another problem is that lamps age with use, i.e., the irradiance emittedby a lamp or its intensity diminishes as the lamp is used. An integratorcan be used to compensate for lamp aging to a certain degree, but eitherthe exposures become too long or is insufficient to provide desireddegree of photochemical reaction in the photosensitive element. Exposureapparatuses for photosensitive elements are known to have a radiationintegration system, sometimes referred to as an integrator, whichevaluates the intensity of the lamps illuminating the exposure bed wherethe printing form lies. An example of an exposure unit having anintegrator is the CYREL® 1000ECLF. The integration system compensatesthe time of exposure according to the intensity of the radiation emittedby the lamps. The system may include a photocell that senses theradiation incident thereon, and a circuit that integrates a signal fromthe photocell. The photocell in these exposure units typically measuresthe intensity of the lamps for a broad spectrum of wavelengths of theemitted radiation. Such exposure control systems, should in theoryprovide the designed for exposure values. In practice however, sinceexposure is a function of many variable factors, there is potential forthe exposure values actually produced by any such system to vary fromthe values designed for. Ultimately the integration of the lamp energyis not sufficient and all the lamps will need to be removed and replacedwith new lamps. Even when the lamp or lamps are replaced, the lightintensity drops off in the first 20 hours of lamp life, so thatrecalibration is necessary throughout this initial age-in of the lamps.Factors which affect the replacement of lamps are the physical locationof the lamps within the hood, their elapsed operation time, and theelapsed operation time of all adjacent lamps. Frequent recalibration dueto lamp replacement is an undesired step that can consume considerableplatemaking time and manpower, as well as printing forms. Due to theproblems and costs associate with lamp changes it is desirable to extendthe life of the lamps without sacrificing uniformity and consistency inirradiation emitted by the lamps during exposure.

Therefore, there is a need to overcome the problems of related art andto provide an improved exposure apparatus and method for preparingrelief printing forms from photosensitive elements using the exposureapparatus. It is desirable to insure proper exposure of photosensitiveelements consistently over the useful life of the lamp/s in an exposureunit. It is also desirable to avoid the time, manpower, and materialsassociated with lamp replacement and recalibration of exposure unit todetermine appropriate exposure for photosensitive elements. It is alsodesirable to extend the lifetime of the lamps without sacrificing thequality and uniformity of the exposure radiation. It is also desirableto insure proper exposure of photosensitive elements necessary toachieve satisfactory resulting relief structures for printing forms.There is a need to establish and maintain conditions in an exposureapparatus that can provide sufficiently consistent quality anduniformity of actinic radiation impinging photosensitive elements.

SUMMARY

In accordance with the present invention there is provided an exposureapparatus for exposing a photosensitive element to actinic radiationcomprising: an exposure bed; an assembly for controlling temperature ofthe bed; and a lamp assembly. The exposure bed includes a first side anda second side opposite the first side, the first side of the bed has anexterior surface for supporting the photosensitive element, the exteriorsurface having at least one orifice that is connected to a means forremoving air between the photosensitive element and the exteriorsurface. The assembly for controlling temperature of the bed allows forheating and cooling that is adjacent the second side of the bedcomprising at least one coil having fluid transported therein, and ameans for adjusting temperature of the fluid. The lamp assembly isdisposed above the bed comprising at least one lamp positioned toirradiate the photosensitive element supported on the exterior surfacewith the actinic radiation.

In accordance with another aspect of the present invention there isprovided a method for exposing a photosensitive element to actinicradiation comprising: supporting the photosensitive element on anexterior surface of a first side of an exposure bed wherein the bed hasa second side opposite the first side and at least one orifice from theexterior surface; removing air between the photosensitive element andthe exterior surface through the at least one orifice; determining atemperature of the bed; controlling the temperature of the bed to atarget temperature by transporting a fluid through at least one coiladjacent the second side of the bed; and, adjusting a temperature of thefluid by heating the fluid and cooling the fluid.

In accordance with another aspect of the present invention there isprovided a a method for preparing a relief printing form from aphotosensitive element having a layer of a photopolymerizablecomposition comprising: imagewise exposing the photosensitive elementthrough a mask to actinic radiation according to the above method forexposing the photosensitive element, forming at least a cured portionand at least a uncured portion of the layer; and treating the exposedelement to remove the uncured portions thereby forming a reliefstructure suitable for printing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view of one embodiment of an apparatusfor exposing a photosensitive element according to the presentinvention, showing a lamp housing assembly and a base assembly having anexposure bed for supporting a photosensitive element having planar orplate-like shape, and showing an upright housing with a portion of acover panel cutaway to show some of a carriage assembly that moves thelamp housing assembly.

FIG. 2A is a schematic front view of one embodiment of the exposureapparatus shown in FIG. 1, showing that the lamp housing assembly ismovable from a first or upper location that is positioned at a distancefrom the base assembly to a second or lowered location (in phantomlines) that is disposed above the photosensitive element on the exposurebed of the base assembly. The second position of the lamp housingassembly may also be referred to as an exposing position or exposurelocation.

FIG. 2B is a schematic back view of one embodiment of the exposureapparatus shown in FIG. 1, showing the lamp housing assembly in thefirst position and the second position (in phantom lines).

FIG. 3A is a schematic side view of one embodiment of the exposureapparatus shown in FIG. 1, taken along line 3A-3A of FIG. 2A in whichthe lamp housing assembly is in the first position, showing oneembodiment of the lamp housing assembly that includes one embodiment ofa lamp assembly having at least one lamp and at least one ballast, andone embodiment of an air distribution assembly having an air chamber andat least one blower; and, one embodiment of the base assembly thatincludes one embodiment of a movable sensor for determining irradianceof the at least one lamp, one embodiment of an exposure bed, and oneembodiment of a means for controlling the temperature of the exposurebed.

FIG. 3B is a schematic side view of one embodiment of the exposureapparatus shown in FIG. 1, taken along line 3B-3B of FIG. 2A in whichthe lamp housing assembly is in the second position, showing the movablesensor in a rotated position interposed in the lamp housing assembly.

FIG. 4 is a schematic exploded view of one embodiment of the lamphousing assembly of the exposure apparatus of FIG. 3A, showing housingcovers, a sheet of glass, a plurality of tubular lamps that are adjacentand substantially parallel to each other, a bottom panel of the airchamber in which the bottom panel is a sheet that includes openings, alayer of an air dispersing medium, and a plurality of ballasts for thelamps.

FIG. 5 is a schematic partial cross-sectional front view of a section ofthe lamp housing assembly and a section of the base assembly taken alongline 5-5 of the one embodiment of the exposure apparatus of FIG. 3B,wherein the sections shown are approximately half sections that can besubstantially replicated (except for the movable sensor) about thecenterline 51 (mixed dashed line) of FIG. 5, that shows the lamp housingassembly in the second position adjacent exposure bed and the means forcontrolling the temperature of the bed of the base assembly, wherein thephotosensitive element is broken apart to show a home position and ahome station of the movable irradiance sensor.

FIG. 6A is a schematic backside view of one embodiment of the exposureapparatus of FIG. 2B with most of the housing covers removed, and with aback ventilation panel of the upright housing is exploded away showingthe carriage assembly as a means for moving the lamp housing assemblyfrom the first position to the second position wherein the lamp housingassembly is in the first position, and showing a means for pressurizingthe air chamber of the lamp housing assembly that includes two blowerseach having intake ducts.

FIG. 6B is a schematic backside view of one embodiment of the exposureapparatus of FIG. 2B with most of the housing covers removed, whereinthe lamp housing assembly is in the second position, showing thecarriage assembly as means for moving the lamp housing assembly from thefirst position to the second position, and showing each of the intakeducts of the two blowers mating with a filter for incoming air duringexposure.

FIG. 7A is a schematic perspective view of one embodiment of a transportassembly for the movable irradiance sensor of the base assembly.

FIG. 7B is a schematic planar top view of the transport assembly and themovable irradiation sensor shown in FIG. 7A, showing the rotatedposition of the movable irradiance sensor.

FIG. 8 is a schematic exploded view of one embodiment of the baseassembly of the exposure apparatus of FIG. 3A, showing a partialcut-away view of the photosensitive element supported on the exposurebed and one embodiment of the means for controlling the temperature ofthe exposure bed that includes an assembly of at least one coil having afluid transported therein to allow for heating and cooling of theexposure bed, and a means for adjusting the temperature of the fluid inthe coil.

FIG. 9 is a schematic planar top view of one embodiment of the exposurebed of the base assembly embodiment of FIG. 8, showing an exteriorsurface of the exposure bed having at least one orifice connecting toone or more channels as means for removing air from between thephotosensitive element (not shown) and the exterior surface of theexposure bed.

FIG. 10A is a schematic diagram of one embodiment of the fluid flow ofthe temperature-controlling assembly of the exposure bed of FIG. 8,showing one or more coils for transporting the fluid that is connectedto a manifold and a reservoir, which is in fluid connection with aheater and a chiller for the fluid.

FIG. 10B is a schematic diagram of another embodiment of the fluid flowof the temperature-controlling assembly of the exposure bed of FIG. 8,showing one or more coils for transporting the fluid that is connectedto a manifold and a reservoir, which is in fluid connection with aheater and a chiller for the fluid.

FIG. 11 is a schematic diagram of one embodiment of a simplified processcontrol chart for an exposure apparatus that can use either or both oftwo independent embodiments of controlling output of one or more lampsin a method for exposing the photosensitive element. In one embodimentthe exposing method includes controlling the air impinging one or morelamps with a programmable logic controller that is connected to blowersvia a motor controller, and to a sensor for measuring temperature of thelamp/s, and/or to a sensor for measuring irradiation of ultravioletradiation output from the lamp/s. In the other embodiment, the exposingmethod includes adjusting output of a lamp irradiation with anadjustable ballast and with a sensor measuring irradiation output fromthe lamp by the use of the programmable logic controller that isconnected to the lamp/s, the adjustable ballast, and the irradiationsensor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Throughout the following detailed description, similar referencecharacters refer to similar elements in all figures of the drawings.

The present invention provides an apparatus and method for exposing aphotosensitive element to radiation, i.e., actinic radiation. Theapparatus may also be referred to herein as a bed exposure unit, aflat-bed exposure unit, or an exposure apparatus. The present exposureapparatus and method may be used for imagewise exposure, blanket oroverall exposure, overall exposure through the back side to form afloor, post-exposure, and/or light-finishing exposure of thephotosensitive element. In most embodiments, the present exposureapparatus and method is used for imagewise exposure of thephotosensitive element. Although in some embodiments the presentapparatus and method is described in reference to a particularembodiment in which the photosensitive element is planar or plate-shapedelement, the invention is not so limited and is also contemplated foruse in exposure apparatuses that accommodate cylindrically-shapedphotosensitive elements.

The present invention provides at least three novel and unobviousembodiments of an exposure apparatus for exposing a photosensitiveelement to radiation. The present invention also provides at least threenovel and unobvious embodiments of a method for exposing aphotosensitive element to radiation. The present invention furtherprovides one or more novel and unobvious embodiments of a method forcontrolling radiation emitting from a lamp in an exposure apparatus forexposing a photosensitive element to the radiation. Specific embodimentsof the present invention of an exposure apparatus and method forexposing include, but are not limited to, the following.

Embodiment One

An exposure apparatus includes, but is not limited to, an exposure bedhaving at least one orifice that is connected to a means for removingair between the photosensitive element and an exterior surface of theexposure bed; an assembly for controlling temperature of the bed toallow for heating and cooling of the bed; and, a lamp assembly having atleast one lamp positioned to irradiate the photosensitive element.

Embodiment Two

A method includes, but is not limited to, the steps of supporting thephotosensitive element on an exposure bed having at least one orificefrom an exterior surface of the bed; removing air between thephotosensitive element and the exterior surface through the at least oneorifice; determining a temperature of the bed; and controlling thetemperature of the bed to a target temperature by transporting atemperature-controlled fluid adjacent a surface of the bed opposite theexterior surface, and heating or cooling the fluid.

Embodiment Three

An exposure apparatus includes, but is not limited to, a lamp assemblyincluding at least two lamps each having a tubular length and abackside, the at least two lamps are adjacent to each other to irradiatethe photosensitive element with radiation; an air distribution assemblyincluding an air chamber disposed adjacent to the backside of the atleast two lamps and having one or more openings that are alignedparallel to the tubular length of the backside for each of the at leasttwo lamps, wherein the chamber is pressurized to provide the same orsubstantially the same volumetric rate of the air exiting each openingand impinging the backside of each of the lamps; a controller connectedto the at least one blower to adjust the volumetric rate of the airimpinging the at least two lamps, and a sensor that is selected fromeither or both; a sensor for measuring a temperature of at least one ofthe lamps, wherein the volumetric rate of the air is adjusted based oncomparison of the measured temperature to a target temperature; or, asensor for measuring irradiance emitting from at least one of the lamps,wherein the volumetric rate of the air is adjusted based on comparisonof the measured irradiance to a target irradiance.

Embodiment Four

The method includes, but is not limited to, the steps of irradiating thephotosensitive element with radiation from at least two lamps adjacentto each other, each lamp having a tubular length and a backside;impinging air on the backside of each of the at least two lamps at avolumetric rate from an air chamber that is adjacent the backside of theat least two lamps and has one or more openings that are alignedparallel to the tubular length for each of the at least two lamps,wherein the air in the chamber is pressurized to uniformly distributethe air exiting each of the one or more openings; controlling thevolumetric rate of the air impinging the at least two lamps by selectingfrom measuring a temperature of at least one of the lamps, and adjustingvolumetric rate of air exiting the one or more openings based on themeasured temperature relative to a target temperature; or, measuringirradiance of at least one of the lamps, and adjusting the volumetricrate of the air exiting the one or more openings based on the measuredirradiance relative to a target irradiance; or measuring both atemperature of at least one of the lamps and irradiance of at least oneof the lamps, which can be the same or different, and adjustingvolumetric rate of air exiting the one or more openings based on themeasured temperature relative to a target temperature and based on themeasured irradiance relative to a target irradianc.

Embodiment Five

An exposure apparatus includes, but is not limited to, an exposure bed;a lamp assembly disposed adjacent the exposure bed that includes atleast two lamps that are adjacent to each other to irradiate the bedwith the radiation; and an adjustable ballast connected to at least onelamp of the at least two lamps to adjust power received by the one lamp;a sensor disposed adjacent at least one lamp of the at least two lampsfor measuring irradiance; a controller that adjusts the power to theadjustable ballast which adjusts the irradiance emitted from the atleast one lamp to match the target irradiance.

Embodiment Six

A method includes, but is not limited to, the steps of irradiating anexposure bed with radiation using a lamp assembly that includes at leasttwo tubular lamps that are adjacent each other, and an adjustableballast connected to at least one lamp of the at least two lamps whereinthe ballast adjusts power received by the one lamp; measuring irradiancefrom the one lamp of the at least two lamps in proximity of the exposurebed; and adjusting the power to the ballast of one lamp based oncomparison of the measured irradiance to a target irradiance to adjustthe irradiance emitted from the at least one lamp to match the targetirradiance.

Any of the above Embodiments One through Six can be combined with one ormore of the other Embodiments, so long as they are not mutuallyexclusive. The skilled person would understand which embodiments weremutually exclusive and would thus readily be able to determine thecombinations of embodiments that are contemplated by the presentapplication.

“Actinic radiation” refers to radiation capable of initiating reactionor reactions to change the physical or chemical characteristics of aphotosensitive composition. Actinic radiation can include ultravioletradiation, visible light, and e-beam radiation. In one embodiment,actinic radiation refers to radiation having wavelengths in theultraviolet region. In another embodiment, actinic radiation refers toradiation having wavelengths in the visible region. In anotherembodiment, actinic radiation refers to radiation having wavelengths inthe ultraviolet and visible regions. Examples of ultraviolet radiationas actinic radiation include, but is not limited to, UV-A radiation,which falls within the wavelength range of from 320 nanometers (nm) to400 nm; UV-B radiation, which is radiation having a wavelength fallingin the range of from 280 nm to 320 nm; UV-C radiation, which isradiation having a wavelength falling in the range of from 100 nm to 280nm; and UV-V radiation, which is radiation having a wavelength fallingin the range of from 400 nm to 800 nm.

“Absorption peak” or “peak activating radiation” refers to a wavelengthor frequency at which a material absorbs the most power whenever thematerial is bombarded with light waves. “Absorption spectrum” refers toan array of absorption lines and absorption bands that results from thepassage of radiant energy from a continuous source through an absorbingmedium.

“Emission peak” or “peak emission” refers to a wavelength or frequencyat which a source of radiation emits the most power.

“Emission spectrum” refers to electromagnetic spectrum produced whenradiations from any emitting source, excited by any of various forms ofenergy are dispersed.

“Irradiance” refers to the power of electromagnetic radiation per unitarea incident on a surface, and is expressed in Watts/meter², ormWatts/cm². In particular for the present invention, the electromagneticradiation is the radiation capable of initiating reaction or reactionsto change physical or chemical characteristics, i.e., actinic radiation,per unit area incident on the photosensitive element. Irradiance mayalso be referred to herein as intensity of the radiation.

The term “room temperature” or, equivalently “ambient temperature,” hasits ordinary meaning as known to those skilled in the art and typicallyincludes temperatures within the range of about 16° C. (60° F.) to about32° C. (90° F.).

The photosensitive element includes a composition layer that may be inan uncured state, a cured state, or in a partially cured state. In someembodiments, the photosensitive element includes a layer of acomposition that is responsive to actinic radiation, i.e.,photosensitive, and thus the composition layer of the photosensitiveelement is uncured or not crosslinked, prior to exposure by the presentinvention. In most embodiments, the photosensitive element includes amask on or adjacent to its exterior surface for exposure of thephotosensitive composition layer to be an imagewise exposure. The maskmay be formed by any method conventional to those skilled in the art. Inother embodiments, the photosensitive element may be blanket exposed inthe present apparatus to overall cure or crosslink the photosensitivecomposition layer. The overall cured photosensitive element may besubsequently engraved to form a relief surface suitable for printing. Inother embodiments, a relief surface on the photosensitive element may beexposed in the present apparatus to light-finish or detackify the reliefsurface formed from a layer of a photosensitive composition that wasexposed to actinic radiation and thus cured, i.e., photohardened orcrosslinked. In yet other embodiments, the photosensitive elementincludes a relief surface formed from a layer of a composition that wasexposed to actinic radiation and is substantially cured, but is stillresponsive to actinic radiation, and thus may be exposed to actinicradiation by the present apparatus to complete curing, i.e.,crosslinking, of the relief surface, which may be referred to aspost-exposure. The photosensitive element may also be referred to hereinas a photopolymerizable element, a photosensitive precursor, a printprecursor, or a precursor.

Exposure Apparatus

FIG. 1 shows one embodiment of an exposure apparatus 10 for exposing aprecursor 20 in accordance with the invention that includes a baseassembly 12, and a lamp housing assembly 14. The base assembly 12 andthe lamp housing assembly 14 each include multiple cover panels 16 thatconnect to a frame or frames to enclose the operational features of theexposure apparatus 10. The base assembly 12 includes an exposure bed 25having a first side 26 with an exterior surface 28 for supporting thephotosensitive element or precursor 20. In most embodiments theprecursor 20 is centered or centrally located on the exposure bed 25.The lamp housing assembly 14 includes at least one blower 30, and atleast one lamp 32 in some embodiments of the apparatus 10, or at leasttwo lamps 32 in other embodiments of the apparatus 10, for exposing theprecursor 20 to actinic radiation at an exposure location. The presentexposure apparatus 10 and method is useful and provides particularadvantages for conventional digital workflow in which the precursorincludes an in-situ mask and is imagewise exposed through the in-situmask in the presence of atmospheric oxygen.

The present exposure apparatus 10 and methods can also be useful formodified digital workflow and analog workflow, provided that thenecessary features for each of these workflows are incorporated into theapparatus. The exposure apparatus 10 includes as an embodiment one ormore of the following features that are described herein, alone or inany combination, a temperature-controlled exposure bed; and/or, a lampassembly having an air distribution assembly for controlling temperatureand/or irradiance of at least one lamp; and/or, lamp assembly includingan adjustable ballast coupled to one or more lamps that adjusts thepower received by the lamp or lamps, for exposing the precursor toactinic radiation. In most embodiments, the exposure apparatus 10includes all of these features for exposing the precursor to actinicradiation, such as ultraviolet radiation, through a mask, i.e.,imagewise exposure. In other embodiments, the exposure apparatus 10includes one or a combination of two of these features. Optionally, theexposure apparatus capable of imagewise exposure with one or more of thefeatures can include an additional exposure station that accommodateslight-finishing and/or post-exposure. In the embodiment shown in FIG. 1,the base assembly 12 includes two drawers 13 a,13 b to accommodate theoptional exposure for light-finishing exposure and/or post-exposure ofthe precursor, in which one drawer 13 a includes lamps (not shown) thatemit UV-C and/or lamps (not shown) that emit UV-A radiation, and thesecond drawer 13 b holds the precursor for exposure/s. For simplicity,the details and the interiors of drawers of the additional exposurestation are not shown. The base assembly 12 and the lamp housingassembly 14 is described in greater detail below.

In the embodiment shown in FIG. 1, between a back side of base assembly12 and a back side of the lamp housing assembly 14 is a upright housing35 having a carriage assembly 36 that supports the lamp housing assembly14 in a cantilevered manner above the base assembly 12, and moves thelamp housing assembly 14 to and from at least two locations. Thisembodiment of the exposure apparatus 10 may be referred to as a top-liftexposure apparatus. In FIG. 1 a portion of a cover panel 16 of theupright housing 35 is removed to show the carriage assembly 36 thatincludes two upright members 38, which are orthogonal to the base andlamp housing assemblies 12,14, and a means for moving the lamp housingassembly 40 on the upright members 38. At a top of the upright housing35 and at the back side of the lamp housing assembly 14 are linearbearings each of which engage with one of the upright members 38 so asto slide or move along the upright member.

The carriage assembly 36 including the means for moving 40 the lamphousing assembly 14 is shown in FIG. 1, FIG. 2A, FIG. 2B, FIG. 6A, andFIG. 6B. The means for moving 40 the lamp housing assembly 14 isconfigured to move the lamp housing assembly which includes a drivemotor 41 operating a gear box 42 connected to a rod 44. At each end ofthe rod 44 is a sprocket wheel 46 a that engages with a toothed belt orgear belt 48. A second rod 49 having ends with sprocket wheels 46 b,which also engage with the gear belt 48, is mounted at or near a top ofthe upright housing 35. A linear bearing 50 is mounted for verticaltransport on each of the upright members 38. The linear bearing 50includes a housing that is coupled to the gear belt 48 and that ismounted to the frame of the lamp housing assembly 14. The lamp housingassembly 14 is moved up and down along the upright members 38 byoperating the drive motor 42 causing the gear box 42 to rotate the rod42 with the sprocket wheels 46 a engaged in the gear belt 48. Since thegear belt 48 travels about sprocket wheels 46 a,46 b, and is coupled tothe linear bearing 50, the linear bearings 50 are moved along theupright members 38, and thereby transports the lamp housing assembly 14to and from a first location, Lh and a second location, Le. The firstlocation Lh of the lamp housing assembly 14 is a home location, that isseparated from the base assembly 12 as shown in FIG. 1 and FIG. 2A toallow for loading of the precursor 20 on the exposure bed 25. The secondlocation Le of the lamp housing assembly 14 is an exposure location, inwhich the lamp housing assembly 14 is disposed above, adjacent to and inclose proximity to the exposure bed 25 as shown in phantom lines inFIGS. 2A and 2B. In the exposure location Le, the at least one lamp 32of the lamp housing assembly 14 is parallel to the precursor 20 on theexposure bed 25.

FIG. 5 shows the lamp housing assembly 14 in the second position Leadjacent to the exposure bed 25 of the base assembly 12 wherein thesections shown are approximately half sections of the lamp housingassembly and the exposure bed 25 and the assembly 65 for controlling thetemperature of the bed that can be substantially replicated (except forthe movable sensor 70) about the centerline 51 (mixed dashed line) ofFIG. 5. The lamp housing assembly 14 further includes a perimeter safetyswitch bar 52 that deactivates the movement of the lamp housing assembly14 should the safety switch bar 52 be contacted or contact an uppersurface of the base assembly 12. When in the exposure position, Le, thehousing of the lamp housing assembly 14 with the safety switch bar 52surrounds the exposure bed 25 and encloses the precursor 20. The coverpanels of the lamp housing prevent or substantially prevent radiationfrom escaping during an exposure. In some embodiments, the safety switchbar is a safety rail connected to a switch that stops the travel of thelamp housing assembly 14 toward the base assembly 12.

In some embodiments as shown in FIG. 5, the lamp housing assembly 14further includes a perimeter seal 53 that has a smaller perimeter thanthe safety switch bar 52. The perimeter seal 53 with one or morestructural elements of the lamp housing assembly 14, such as theoptional glass plate 110 that resides on a frame member, and with theupper surface of the base assembly 12 form an enclosure 58 for amodified digital workflow. The workflow for the modified digitalexposure creates an environment of an inert gas and a concentration ofoxygen of 190,000 to 100 ppm in the enclosure 58 for imagewise exposureof the precursor having an in-situ mask, as disclosed in U.S. Pat. Nos.8,241,835 and 8,236,479.

The exposure apparatus 10 further includes a main switch 54 and acontrol panel 55 having a display and a series of selectors for enteringinformation by the operator about the precursor to be exposed, and formonitoring and controlling its operation. The exposure apparatus 10 alsoincludes at least one controller 56 (shown in phantom lines), or acomputer and regulator/s, that is electronically coupled to componentsof the exposure apparatus 10 and with the aid of sensors, monitorscertain specific conditions in the exposure apparatus 10, compares eachmonitored condition to a desired or target value, and then as needed mayperform or cause to be performed an action to change the currentcondition. In most embodiments, the controller 56 is a programmablelogic controller, sometimes referred to as PLC or programmablecontroller, which is a digital computer used for automation, such ascontrol, sequencing, and interlock logic, of the electromechanicaldevices contained herein. In another embodiment of the exposureapparatus (not shown), the lamp housing assembly can be attached to thebase assembly by one or more hinges connecting to a common side of eachassembly, which can be referred to as a clamshell exposure unit. For theloading of the precursor on the exposure bed, the lamp housing assemblypivots by the hinge/s and tilts away from the base. For the exposurelocation, the lamp housing assembly would pivot toward the base, so thatthe at least one lamp of the lamp housing assembly would be parallel tothe precursor on the exposure bed.

Base Assembly

As shown in FIG. 3A, FIG. 3B, FIG. 5, and FIGS. 8-10, the base assembly12 further includes the exposure bed 25 having the first side 26 and asecond side 27 opposite the first side 26, a means 60 for removing airbetween the precursor and an exterior surface on the first side 26 ofthe exposure bed 25, and an assembly 65 for controlling temperature ofthe exposure bed 25 to allow for heating and cooling of the exposurebed, and thereby heating and cooling of the precursor 20.

In the embodiments shown the apparatus 10 accommodates conventionaldigital workflow, which is conducted in the presence of atmosphericoxygen, as well as modified digital workflow. The exposure bed 25includes an array of ports 66 to introduce an inert gas, such asnitrogen, and compressed air, in the enclosure 58 and create a desiredenvironment of the inert gas and concentration of oxygen of between190,000 ppm and 100 ppm, for the modified digital imagewise exposurethat is disclosed in U.S. Pat. No. 8,241,835. Although it is preferredthat the exposure apparatus 10 is includes the ports 66 and gas suppliesof nitrogen 68 a and compressed air 68 b and lines to be able to conductmodified digital imagewise exposures of precursors, this capability isoptional and the present inventive exposure apparatus 10 and methods donot rely upon this capability. In some embodiments during imagewiseexposure, the gases in the enclosure 58 can leak at the seal 53 andescape to interior of the apparatus 10, which is ultimately vented intothe room or outside.

Near the backside of the exposure bed 25 and adjacent to the uprighthousing 35 is a scanning sensor 70 for determining the irradiance thatemits from one or more lamps 32 of the lamp housing assembly 14. Asshown in FIG. 1, the scanning sensor 70 is located at its home stationSh. The scanning sensor 70 includes a transport assembly 62 for movingthe scanning irradiance sensor 70 from one to two or more positionsalong a passage that is near the upright housing 35 at the backside ofthe exposure bed 25. Though physically located with the base assembly12, the transporting assembly 72 and the scanning irradiance sensor 70will be further described in relation to the lamp housing assembly 14and methods of operating the lamps.

In one embodiment of the present exposure apparatus 10 and method ofuse, it is desirable to maintain the precursor 20 at a constant orsubstantially constant temperature or within a small range oftemperature during exposure, i.e., from start to end of an exposure tothe radiation by the lamp 32 or lamps of the lamp assembly 14. Thequality of the relief image can be improved by maintaining thetemperature of the precursor constant or substantially constant duringexposure, i.e., from the start until the end of the irradiance by thelamp or lamps. In most embodiments the temperature of the precursor 20during exposure is maintained at a target temperature less than about35° C. In some embodiments the precursor 20 is maintained at a targettemperature between and optionally including any two of the followingvalues 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, and35° C. In some other embodiments during exposure the precursor 20 ismaintained constant or substantially constant in a small temperaturerange that is ±3° C. from a temperature selected from 20 to 35° C. Inmost embodiments, the precursor 20 is allowed to equilibrate to thetarget temperature before exposure begins, and then is maintained at thetarget temperature, or within the target temperature range, during theexposure, and to completion of the exposure.

The exposure bed 25 is made of metal since its thermal conductivityallows the exposure bed to quickly respond to adjustments by thetemperature-controlling assembly 65 to maintain the temperature of thebed at the target temperature or in the target temperature range, sothat the precursor 20 is maintained at its target temperature. In someembodiments, the exposure bed 25 is made of aluminum. In some otherembodiments, the exposure bed 25 is made of aluminum that is embeddedwith copper plate/s. The temperature controlling assembly 65 for theexposure bed 25 that allows for heating and cooling of the exposure bed,in combination with the means 60 for removing air from between theprecursor 20 and the exterior surface 28 of the exposure bed that bringsthe precursor into intimate contact with the exterior surface,establishes the precursor at a target temperature or in a temperaturerange prior to exposure and maintains the precursor at a targettemperature or in a target temperature range during exposure. Inembodiments in which the exposure apparatus 10 is used for imagewiseexposure of the precursor 20, the back side 21 or side with the supportfor the photosensitive precursor contacts the exterior surface 28 of thebed. The capability to have the precursor 20 in intimate contact withthe exposure bed 25 that can be heated and cooled allows for thetemperature of the precursor to be maintained regardless of the ambientconditions and counters the warming effect by the lamp or lamps on theprecursor. This capability also allows for adjusting or optimizing thetarget temperature of the exposure bed 25 according to the particulartype of precursor that is being exposed, i.e., precursors havingdifferent photosensitive compositions, and/or additional layers, and/orfor treatment by heat or solution.

In some embodiments, the temperature of the precursor 20 can be taken atone or more locations on the precursor and can be measured by one ormore infrared sensors (not shown). In most embodiments, the temperatureof the precursor 20 is not directly measured, but the temperature of theexposure bed 25 is measured with a sensor 73, to thereby maintain theprecursor at the desired temperature. The temperature of the exposurebed 25 is established prior to exposure and during exposure ismaintained at a target temperature less than about 38° C., and typicallyis is established and maintained at a target temperature or in a targettemperature range between 20 to 35° C. In some embodiments, the exposurebed 25 is established and maintained at a target temperature between andoptionally including any two of the following values 20, 21, 22, 23, 24,25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, and 38° C. In someother embodiments, the exposure bed 25 is maintained constant orsubstantially constant in a target temperature range that is ±2° C. froma temperature selected from 24 to 31° C. In one embodiment, the measuredtemperature of the exposure bed 25 is offset from the actual temperatureof the precursor 20. However, through testing the offset between the twotemperatures, i.e., temperature of the exposure bed and the temperatureof the precursor, is known and compensated for by setting the targettemperature of the exposure bed 25 to provide the desired targettemperature for the precursor 20 for and during exposure. In someembodiments, the temperature of the precursor 20 when positioned on theexposure bed 25 readily equilibrates to the target temperature of theexposure bed. This can occur when the precursor 20 is stored at roomtemperature and/or when the precursor has a thickness (i.e., of thephotopolymer layer and the support) that is relatively thin, i.e.,typically less than 112 mils (0.28 cm).

The exterior surface 28 of the exposure bed 25 includes at least oneorifice 74 that is connected to the means 60 for removing air betweenthe precursor 20 and the exterior surface, such as a vacuum source. Theat least one orifice 74 is centrally located on the exposure bed 25, sothat precursors of any size, i.e., planar area, when located on theexposure bed covers all of the one or more orifices 74. The number oforifices 74 is not particularly limited providing that the air betweenthe precursor 20 and the exterior surface 28 of the exposure bed 25 canbe sufficiently removed to provide uniform or substantially uniformcontact of the precursor to the exterior surface, and does not trappockets of air between the precursor and the exterior surface. Too fewof orifices may require excessive vacuum to remove the air, and/or maydraw the precursor 20 into the orifice 74 which can result in artifact/sbeing formed in the precursor or artifact that appear after additionalpreparation steps to convert the precursor into a printing form. Toomany orifices can affect the ability of the exposure bed 25 to maintainits temperature and/or disrupt its substantially uniform exteriorsurface that supports and contacts the precursor 20, and as such it maybe difficult to maintain the temperature of the precursor substantiallyconstant during exposure. In one embodiment, the exposure bed 25includes four orifices 74 that are uniformly and geometrically spacedapart and centrally located on the exterior surface 28. Two or moreorifices 74 do not necessarily need to be geometrically or uniformlyspaced apart provided that the air can be uniformly removed withouttrapping air between the precursor 20 and the exterior surface 28. Inmost embodiments, the at least one orifice 74 forms an air passage 75from the first side 26 to the second side 27 of the exposure bed 25; anda coupling 76 is located at an end of the passage 75 on the second side27 of the bed, which connects the orifice 74 via an air conduit 77 ortubing to the vacuum source 79 as the means 60 for removing air frombetween the precursor and the bed 25. The means 60 for removing airbetween the precursor 20 and the exterior surface 28 is a source forcreating a vacuum or negative pressure, which in most embodiments is avacuum pump. It is well within the skill of one in the art tocontemplate alternate embodiments of the means 60 for removing air thatcan be configured to remove air between the precursor 20 and theexposure bed 25, such as for example, a blower operating to provide anegative pressure, or a venturi, or a house vacuum for variousoperations conducted at a site or facility.

Optionally, in one embodiment the first side 26 of the exposure bed 25includes one or more channels 78 that connect to at least one of theorifices 74. The one or more channels 78 are grooves into the exteriorsurface 28 of the bed 25 that form pathways to direct air to the one ormore orifices 74 and facilitate the removal of air from between theprecursor 20 and the exterior surface 28. Each of the one or morechannels 78 has a depth and a width at the exterior surface 28 of thebed 25. The channel depth is not particularly limited, though in mostembodiments the channel 78 can have a depth of 0.5 to 1.1 mm. Thechannel width should not be so wide that the precursor 20 is pulled intothe channel 78 when the air is removed between the precursor and theexterior surface 28 by the vacuum source 60 as this can form artifactsin the precursor. The channel 78 has a width that is between andoptionally including any two of the following values 0.5, 0.6, 0.7, 0.8,0.9, 1.0, 1.1, 1.2, 1.3, 1.4, and 1.5 mm. In some embodiments, the widthof the channel 79 is 1.0 to 1.4 mm. If more than one channel 78 ispresent, the width and depth of each channel can be different. Inanother embodiment, optionally the exterior surface 28 of the exposurebed 25 can be textured or roughened to aid in removing air or eliminateentrapping air between the precursor 20 and the exterior surface. Insome embodiments, the exterior surface 28 can include both the channels28 and the textured surface. For small precursors having for example asize less than 220 mm by 250 mm, one orifice 74 can be sufficient toremove air between the precursor 20 and the exterior surface 28. Forlarge precursors having for example, a maximum size of 1067 mm by 1524mm, four orifices 74 in combination with a plurality of connectingchannels 78 may be sufficient to remove air between the precursor 20 andthe exterior surface 28.

When the precursor 20 is located on the exposure bed 25 for an exposure,the one or more orifices 74, and optional channels 78, are covered bythe precursor. It should be noted that in the present invention the oneor more orifices 74 used to remove air and assure intimate contactbetween the precursor 20 and the exterior surface 28, are not intendedfor use in analog workflow in which a negative is brought into intimatecontact to a side of the precursor 20 opposite the support side 21 witha transparent membrane or vacuum foil and drawing vacuum. In analogworkflow, openings for drawing vacuum of the negative to the precursorare located at the perimeter of the exposure bed. In the presentinvention, the central location of one or more orifices 74 used toremove air and assure intimate contact between the precursor 20 and theexterior surface 28 and the position of the precursor over the orifice/s74 would block the ability to draw the necessary vacuum for analogworkflow. The present method of removing air between the precursor 20and the exterior surface 28 of the bed 25 is conducted in the absence ofthe transparent membrane or covering that is used for analog exposureworkflow.

The base assembly 12 includes the assembly 65 for controlling thetemperature of the exposure bed 25 that is adjacent the second side 27of the bed, which heats and cools the bed. The temperature-controllingassembly 65 for the bed 25 includes at least one coil 82 that has afluid transported therein, and a means 84 for adjusting or changing thetemperature of the fluid. In one embodiment, the at least one coil 82 ismounted into contact with the second side 27 of the exposure bed 25 witha silicone-based material that aids with the transfer of heating and/orcooling capacity from the coil 82 to the exposure bed. The coil 82 ismade of metal, and can be for example, copper or aluminum. In mostembodiments, there are two or more coils 82, each of which aresubstantially the same and have a length and a diameter that is thesame, so as to provide uniform flow of the fluid through the coils 82and thus can uniformly maintain coils at the same or substantially thesame temperature. Each of the two or more coils 82 has an entry that isconnected to a manifold 85 for supplying each of the coils with thefluid; and, has an exit to return the fluid into a separated section ofthe manifold.

The temperature controlling assembly 65 for the exposure bed 25 can alsoinclude a reservoir 86 that is interspersed between the fluid entrance83 a to the manifold 85 and the fluid exit 83 b from the manifold. Oneembodiment of fluid flow in the temperature controlling assembly 65 isshown in FIG. 10A. Another embodiment of fluid flow in the temperaturecontrolling assembly 65 is shown in FIG. 10B. The reservoir 86 receivesthe fluid exiting the one or more coils 82 and the section of themanifold 85, and provides the fluid to the manifold. The fluidcontinuously circulates through the one or more coils 82, the manifold85, conduits 90, and the reservoir 86 with the use of one or more pumps87 and valves 92. The means 84 for changing the temperature of the fluidis configured to change the temperature of the fluid transported throughthe coils, which includes a heater 88 and a chiller 89. In theembodiment of FIG. 10A, each of the heater 88 and the chiller 89 isconnected with conduits to the reservoir 86, to receive fluid from thereservoir and return the fluid after it is heated or cooled to thereservoir. In the embodiment of FIG. 10B, the heater 88 and the chiller89 are each connected with conduits 90 to receive fluid from thereservoir 86 and send the fluid to the manifold 85 after it is heated orcooled. This embodiment also provides a separate conduit 90 a and valve92 c for fluid flow between the reservoir 86 and the manifold 85. Themeans 84 for changing the temperature of the fluid can include one ormore pumps 87 for transporting the fluid through the conduits 90, 90 aand the heater 88 and chiller 89. If the exposure bed 25 needs to beheated to maintain its temperature and the precursor 20 at the targettemperature, a valve 92 a is operated to direct the fluid from thereservoir 86 to the heater 88 which raises the temperature of the fluidreturning to the reservoir, which is then supplied to the manifold 85that distributes the fluid to the coils 82. In most instances theheating of the exposure bed 25 occurs prior to start of the exposure,either before or after the precursor 20 is placed on the bed. If theexposure bed 25 needs to be cooled to maintain its temperature and theprecursor 20 at the target temperature, a valve 92 b is operated todirect the fluid from the reservoir 86 to the chiller 89 which lowersthe temperature of the fluid returning to the reservoir, which is thensupplied to the manifold 85 that distributes the fluid to the coils 82.In most instances cooling of the exposure bed 25 occurs during exposureof the precursor 20. In most embodiments the fluid transporting throughthe one or more coils 82 is water. The temperature of the exposure bed25 can be measured by one or more contact sensors 73 or infrared sensorsthat are located in a central location on the second side 28 of theexposure bed. In some embodiments, the temperature of the exposure bed25 is measured at only one location, which is considered representativethe entire exposure bed.

In operation, the lamp housing assembly 14 is in the first location Lhand one or more of the pumps 87 for the temperature controlling assembly65 for the exposure bed 25 are activated to circulate fluid through thecoils 82, the manifold 85, and the reservoir 86. The temperature of theexposure bed 25 is determined with the temperature sensor 73 on thesecond side 27 of the bed, and compared to a target temperature for thebed. The temperature of the bed 25 is controlled to a target temperatureby transporting the fluid through the coils 82, and heating or coolingthe fluid. The exposure bed 25 is established and maintained at itstarget temperature due to the contact of the coils 82 with the secondside 27 of the exposure bed and the thermal conductivity of the fluidand materials of the bed and coils. With particular reference of thefluid flow of the embodiment shown in FIG. 10B, the fluid continuouslycirculates through the coils 82, the manifold 85, conduit 90 a and thereservoir 86 with the use of pump 87 and valves 92 c is open, and valves92 a and 92 b are closed. The programmable logic controller 56 is usedto control the temperature of the exposure bed 25 by appropriateheating, cooling, and recirculating of fluid, as appropriate, throughthe coils 82, conduit 90, and reservoir 86. If the measured temperatureof the bed 25 is less than the target temperature, the means 84 foradjusting the temperature of the fluid is activated, valve 92 c may beclosed, and the valve 92 a is opened to direct the fluid in thereservoir 86 through the heater 88 to supply the manifold 85 and thecoils 82 with warmed fluid, which then returns to the reservoir 86. Ifthe measured temperature of the bed is greater than the targettemperature, the means 84 for adjusting the temperature of the fluid isactivated, valve 92 c may be closed, and the valve 92 b is opened todirect the fluid in the reservoir 86 through the chiller 89 to supplythe manifold 85 and coils 82 with cooled fluid, which then returns tothe reservoir 86 In either condition, the fluid continues to becirculated through the means 84 for adjusting the temperature of thefluid until the exposure bed 25 reaches the target temperature or withinthe target temperature range, at which time the valves 92 a and 92 bclose, and valve 92 c is opened to continue circulation of the fluidthrough the assembly 65 for controlling the temperature of the bed.Typically during exposure of the precursor 20, the exposure bed 25 heatsup, and the means 84 to adjust the temperature of the fluid cooler isactivated to maintain the bed at the target temperature or in the targettemperature range. For example, during an exposure of about 15 minutesat 17-20 mWatts/cm², the temperature of exposure bed 25 and theprecursor 20 could increase as much as 10° C., but for the presence ofthe temperature controlling assembly 65 of the exposure bed.

After the exposure bed 25 has reached its target temperature, theprecursor 20 is placed on the exterior surface 28 of the exposure bed ina central location covering the four orifices 74 and the plurality ofchannels 78. The precursor 20 is stationary and remains in place on theexposure bed 25 during exposure. In one embodiment, the precursor 20includes an in-situ mask, and the precursor is oriented with the in-situmask facing the one or more lamps 32 of the lamp housing assembly 14 forimagewise exposure through the in-situ mask. If the precursor 20 isstored at room temperature, the precursor quickly adjusts to thetemperature of the exposure bed 25 and reaches its target temperature.In some embodiments, the precursor 20 is stored so that the precursorhas a temperature when positioned on the exposure bed that is no morethan about 10° C. from the target exposure bed temperature. In mostembodiments, the precursor 20 is stored so that the precursor has atemperature when positioned on the exposure bed that is no more thanabout 5° C. from the target exposure bed temperature. The greater thetemperature difference between the precursor 20 as it is positioned onthe exposure bed 25 and the temperature of the exposure bed itself, thelonger it will take the precursor to equilibrate to the temperature ofthe bed or reach its target temperature. If the exposure is startedbefore the precursor reaches target temperature some of the advantagesin quality may not be fully realized. To facilitate the precursor 20quickly reaching target temperature or temperature range, the vacuumpump 79 connected to the orifices 74 is activated removing air betweenthe precursor 20 and the exterior surface 28. Depending upon the size ofthe precursor 20 and the number of orifices 74, and optional channels78, it may take up to several minutes to remove the air between theprecursor and the exterior surface through the orifices. In mostembodiments the precursor reaches the target temperature or targettemperature range within 60 seconds after the air is removed between theprecursor 20 and the exterior surface 28 of the exposure bed 25.

The drive motor 41 is activated to transport the lamp housing assembly14 to the second position Le or the exposure position that is adjacentthe uppermost surface of the base assembly 12. Optionally, the lamphousing assembly 14 may undergo one or more steps to assure that the atleast one lamp 32 of the lamp housing assembly 14 is energized to emitradiation at a target condition. The precursor 20 is exposed to theradiation emitting from the at least one lamp 32 with sufficientirradiance to substantially complete the photochemical reaction/s in thecomposition layer of the precursor. During exposure until completed, inmost embodiments, the vacuum pump 79 continues to operate keeping theprecursor 20 in intimate contact with the exterior surface 28 of theexposure bed 25 so that the precursor will quickly respond to changesthat maintain the temperature of the exposure bed at the targettemperature or in the target temperature range.

Lamp Housing Assembly

As shown in FIG. 3A, FIG. 3B, FIG. 4, FIG. 5, FIG. 6A, FIG. 6B, FIG. 7A,FIG. 7B, and FIG. 11, the lamp housing assembly 14 further includes alamp assembly 102 having at least two lamps 32, an air distributionassembly 105, and one or more sensors 107 for measuring or determiningtemperature of at least one lamp 32, and one or more sensors 108 formeasuring or determining irradiance emitted by at least one lamp at awavelength or in a range of wavelengths. As shown in FIG. 4, the lamphousing assembly 14 is assembled with the following orientation ofstructures: an optional glass plate 110; at least two tubular lamps 32for irradiating the precursor 20 with radiation during exposure; a sheet112 forming a base of an air chamber 115 and having at least one opening117 aligned with each of the at least one lamp 32; an optional airdispersing medium 118, at least one ballast 120 for each group of one tofour lamps; a housing cover 122 for the air chamber 115; and, the atleast one blower 30. The glass plate 110 need not be present in allembodiments of the lamp housing assembly 14. In embodiments in which theexposure apparatus 10 also has the capability for exposing a precursor20 according to modified digital workflow, the glass plate 110 isincluded in the lamp housing assembly 14 since the glass forms a top ofan enclosure 58 so that the precursor, which is contained in theenclosure, can be exposed in an environment of an inert gas and adesignated concentration of oxygen. In some embodiments, the lampassembly 102 includes the at least two lamps 32, and the at least oneballast 120. The air distribution assembly 105 includes the sheet 112having at least one opening 117 for each lamp 32, the cover 122, and theat least one blower 30, and optionally the layer of the air dispersingmedium 118. The at least one lamp 32; the at least one ballast 120;sensors 70, 73, 107, 108; at least one blower 30, are energized with apower source (not shown).

In the present exposure apparatus 10, the source of radiation used forexposing the precursor 20 is at least two lamps 32 that are in the formof tubular lamps. In most embodiments, the tubular lamps 32 arefluorescent lamps that include materials which emit sufficient actinicradiation at the wavelength needed for photoreaction of thephotosensitive composition of the precursor 20. Each of the at least twolamps 32 have a tubular length and a backside 130 a, and a front side130 b. The at least two lamps 32 of the lamp assembly 102 are adjacentand parallel to each other. In the embodiment shown, the lamps 32 areoriented with the length of the lamp going from front side to the backside of the exposure apparatus 10. The lamps may be referred to hereinas tubular lamps, or light tubes. The at least two lamps 32 in mostembodiments is a plurality of lamps 132 that because they are adjacentand parallel and form a plane can be considered a bank of lamps. Thebank of lamps may also be referred to as a wall, or an array, or a rowof lamps or light tubes. The number of light tubes in the plurality oflamps 132 is not particularly limited provided that there are asufficient number of tubular lamps 32 to fully irradiate with sufficientuniformity of energy the surface of the precursor 20 to be exposed. Insome embodiments, the number of tubular lamps 32 in the plurality oflamps 132 is from five to fifty. In other embodiments, the number oftubular lamps 32 in the plurality of lamps 132 is from fifteen to forty.The number of tubular lamps 32 in the plurality of lamps 132 in someother embodiments is thirty to thirty-six, and in yet other embodimentsis fourteen to eighteen. In most embodiments, all lamps 32 of theplurality of tubular lamps 132 are energized to emit radiation for anexposure. Energizing all the lamps 32 for every exposure assures thatall lamps in the plurality of lamps 132 age at about the same rate, andthus that the quality of the exposure on precursor 20 is consistent foran extended time of operation of the apparatus 10. In most embodiments,each lamp 32 of the plurality of tubular lamps 132 has power between 60to 140 watts. In one embodiment, each lamp 32 of the plurality oftubular lamps 132 has a length at least as long as a width or length ofthe exposure bed 25. In most embodiments, the lamps 32 of the pluralityof tubular lamps 132 have a length that is longer than the length orwidth of the exposure bed 25. In most embodiments, when the lamp housingassembly 14 is in the exposure position Le, the front side 130 b ofplurality of tubular lamps 132 can be at a distance of about 2 to about6 inches (about 5 to about 15 cm) from a surface of the precursor 20that faces the lamps, i.e., exposed surface. In some other embodiments,the front side 130 b of the plurality of tubular lamps 132 can be at adistance of about 2.4 to about 4 inch (about 6 to 10 cm) from theexposed surface of the precursor 20. The exposure time may vary from afew seconds to many minutes, depending upon the intensity and spectralenergy distribution of the radiation, the distance of the plurality oflight tubes from the precursor, and the nature and thickness of thephotopolymerizable material of the precursor 20.

In one embodiment of the exposure apparatus 10, each lamp 32 or lighttube in the plurality of tubular lamps 132 can emit radiation at thesame or substantially the same wavelength or wavelength range. In thisembodiment, for example, each lamp 32 in the plurality of light tubes132 can emit ultraviolet radiation at wavelengths in the range of 310 to400 nm (which may be sometimes be referred to as ultraviolet-Aradiation, (UV-A)). This embodiment is particularly useful for imagewiseexposing the precursor 20 (through the in-situ mask), blanket exposingthrough the back side of the precursor, and can also be useful forpost-exposing the precursor to complete the photopolymerization process(after relief is formed). A particularly suitable lamp 32 for theplurality of tubular lamps 132 is a 140 Watt fluorescent lamp, Model No.TL140W-10-R (made by Philips Corp., from Amsterdam, Netherlands) forexposing with UV-A ultraviolet radiation. This suitable lamp has anirradiance capacity that is about 17 to about 30 mWatts/cm², which rangeis wider than the irradiance capacity range of many conventionalfluorescent tubular lamps, i.e., typically about 18 to 24 mWatts/cm²,that are used in conventional exposure apparatuses. The wider range ofirradiance capacity by the particularly suitable lamp extends thelifetime at which the lamp emits at the desired irradiance or at thetarget range of irradiance.

In an alternate embodiment of the exposure apparatus 10, the pluralityof light tubes 132 can include at least two types of lamps, wherein eachtype of lamp emits radiation at a different wavelength or range ofwavelengths. In this alternate embodiment, for example, one type of lampin the plurality of light tubes may emit ultraviolet radiation atwavelengths in the range of 310 to 400 nm (UV-A), and another type oflamp in the plurality of light tubes may emit ultraviolet radiation atwavelengths in the range of 200 to about 300 nm, which may be referredto as ultraviolet-c radiation (UV-C)). In most embodiments, the twotypes of lamps would be in alternating positions along the wall of theplurality of light tubes. This embodiment is particularly useful forcombining the steps of post-exposure and finishing exposure to expose atthe same time a precursor 20 that has already been treated to form therelief surface, in which post-exposure completes the polymerizationprocess, and the finishing exposure is used to detackify the reliefsurface of the printing plate. Thus, any one or more of the featuresthat are described herein primarily for use with the imagewise exposureor back exposure of the precursor, can also be used alone or in anycombination, for finishing exposure and/or post exposure, which includesthe temperature-controlled exposure bed; and/or, the lamp assemblyhaving an air distribution assembly for controlling temperature and/orirradiance of at least one lamp; and/or, the lamp assembly including anadjustable ballast coupled to one or more lamps that adjusts the powerreceived by the lamp or lamps, for exposing the precursor to actinicradiation. However, the use of one or more of these features forfinishing exposure and/or post exposure may not have the same advantagesto the precursor as is realized for imagewise exposure.

In most embodiments, the lamp assembly 102 is composed of two or morelamps, i.e., the plurality of lamps 132, in which each lamp 32 ismounted between two sockets (not shown) in a bracket (not shown) to beadjacent and parallel to each other so as to form the bank of lamps;and, a ballast 120 is provided for groups of one to four lamps. In oneembodiment, each lamp 32 is connected to one ballast 120. In anotherembodiment, two lamps 32 are grouped and connected to one ballast 120.In some other embodiment, three lamps 32 are grouped and connected toone ballast 120. In some other embodiment, four lamps 32 are grouped andconnected to one ballast 120. Ballast 120 at least provides thenecessary voltage to start the lamp or group of lamps 32. In someembodiments, the ballast 120 can also be used to stabilize or maintainpower to the lamp 32. In some embodiments of the present apparatus 10,the type of ballast is not limited, and can include for example,electronic and electromagnetic. In one embodiment, the ballast iselectronic ballast.

In some embodiments, the ballast 120 is an adjustable ballast, which mayalso be referred to as a dimmable ballast, that adjusts the powerreceived by the lamp or group of lamps 32. The adjustable ballast 120 isconnected to at least one lamp 32 and controls the power received by theat least one lamp from the power source, by adjusting its voltage. Inmost embodiments the exposure apparatus 10 also includes a ballastdimmer controller (not shown) that interfaces with the adjustableballast/s 120 and the lamp/s 32 to control adjustable ballasts and thelamp output. The adjustable ballast 120 can be provided for groups ofone to four lamps. In the embodiment shown, each lamp 32 of the lampassembly 102 is connected to an adjustable ballast 120. The ballasts 120are mounted on bracket support (not shown) within the air chamber 115above the metal sheet 112. In some embodiments, each adjustable ballast120 can be adjusted to provide about 5 to 100% of the maximum power fromthe power source (not shown) to the lamp or group of lamps 32, i.e., theadjustable ballast allows about 95% to 0% of the power to the lamp/s. Insome other embodiments, each adjustable ballast 120 can be adjusted toprovide about 20 to 100% of the maximum power from the power source tothe lamp or group of lamps 32; i.e., the adjustable ballast allows about80% to 0% of the power to the lamp/s. In yet other embodiments, eachadjustable ballast 120 can be adjusted to provide about 10 to about 80%of the maximum power from the power source to the lamp or group of lamps32; i.e., the adjustable ballast allows about 90% to 20% of the power tothe lamp/s. In still other embodiments, each adjustable ballast 120 canbe adjusted to provide about 30 to about 90% of the maximum power fromthe power source to the lamp or group of lamps 32; i.e., the adjustableballast allows about 70% to 10% of the power to the lamp/s. Adjustmentof the power to the lamp or lamps by the ballast 120, adjusts theirradiance emitting from the lamp or lamps 32. An adjustable ballastthat is suitable for use in some embodiments of the exposure apparatus10 is a Dimmable Electronic Ballast EVL230 available from EckerleIndustrie Elektronik GmbH (Malsch, Germany). In the embodiment shown,the ballasts 120, which can be the adjustable ballasts 120, for thelamps 32 are located within the air chamber 115. The ballasts 120 aremounted on a support frame-like platform (not shown) sufficiently abovethe sheet 112 so as not to block the opening/s 117 of the sheet 112 andto allow for air to flow through the air chamber 115.

Optionally, each lamp assembly 102 can include a transformer (not shown)for pre-heating a coil in the lamp 32. In one embodiment, a transformeris mounted on a side of the bracket opposite the light tube, i.e., abackside of the bracket, and is connected to the socket. The preheatingof the coil of the lamp 32 by the optional transformer typicallyincreases the operational lifetime of the lamp, i.e., extending the timeat which the lamp provides the desired radiation output. In theembodiment shown, the filament pre-heating transformer is included withthe dimmable ballast.

In some embodiments, in order to assure consistent quality of exposure,i.e., the radiation emitted by the plurality of tubular lamps 102 isconsistent, for a single exposure of a precursor, as well as for oneexposure of a precursor to another exposure of a different precursor,i.e., for exposures of multiple precursors over a period of time, eachlamp 32 of the plurality of tubular lamps 132 is maintained at aconstant or substantially constant temperature, or within a temperaturerange. The maintaining of each lamp 32 of the plurality of light tubes132 at a constant or substantially constant temperature or in atemperature range aids in providing consistent quality of radiationemitted for each exposure, and in extending the lifetime of the lamps.In some embodiments, each lamp 32 of the plurality of light tubes 132 ismaintained at a temperature between 30 to 60° C. In most embodiments,each lamp 32 is maintained at less than 55° C., and in particular from40 to 55° C. In some other embodiments, each lamp 32 of the plurality oflight tubes 132 is maintained at a target temperature plus or minus 5°C. The temperature of each lamp 32 of the plurality of light tubes 132can be measured by one or more contact or infrared sensors. In someembodiments, the temperature of only one lamp 32 is measured which isconsidered representative of the temperature of each of the lamps 32 inthe plurality of light tubes 132. In the embodiment shown, the sensor107 for measuring the temperature of a representative lamp 32 is locatedat the backside 130 a of one lamp 32 about midway in the bank of lamps132.

In some embodiments, in order to assure consistent quality of exposure,i.e., the radiation emitted by the plurality of tubular lamps 132 isconsistent, for a single exposure of a precursor, as well as for oneexposure of a precursor to another exposure of a different precursor,i.e., for exposures of multiple precursors over a period of time, eachlamp 32 of the plurality of light tubes 132 is maintained at a constantor substantially constant irradiance, or within an irradiance range. Themaintaining of each lamp 32 of the plurality of light tubes 132 at aconstant or substantially constant irradiance or in an irradiance rangeaids in providing consistent quality of radiation emitted for eachexposure, and in extending or substantially extending the lifetime ofthe lamps. In some embodiments, each lamp 32 of the plurality of lighttubes 132 is maintained at irradiance of about 17 to about 22milliWatts/cm². In most embodiments, each lamp is maintained at anirradiance of about 17 to about 20 mWatts/cm².

The irradiance of each lamp 32 of the plurality of light tubes 132 canbe measured by one or more irradiance sensors 70, 108 a, 108 b. Theirradiance sensors 70, 108 a, 108 b are sensitive to the wavelength orthe range of wavelengths emitted by the lamp/s 32 for the exposure andresponsive to, i.e., measure, the irradiance emitted from the lamp 32.In some cases, the irradiance sensors 70,108 a,108 b measure the peakirradiance emitted from the lamp/s 32. Since the lamp assembly housing14 is in the exposure position Le when the sensors 70,108 a,108 b areactivated, the position of the lamp/s 32 relative to the sensors is thesame or substantially the same and the temperature of the lamp/s ismaintained by the air distribution assembly 105, measurement by theirradiance sensors 70,108 a,108 b will detect changes to the irradianceemitting from the lamp/s 32 that is due primarily to use and aging. Insome embodiments, the irradiance of only one lamp 32 is measured whichis representative of the irradiance of each of the lamps in theplurality of light tubes 132. In one embodiment shown in FIG. 5, astationary irradiance sensor 108 a for measuring the irradiance of arepresentative lamp 32 is located at the front side 130 b of the lamp 32(opposite the backside of one lamp) in the bank of lamps 132. Thestationary irradiance sensor 108 a can be located at substantially anyone lamp 32 of the plurality of lamps 132, and substantially anywherealong the length of one tubular lamp 32, except close to the ends of thetubes 32 or the first or last lamp of the bank of lamps 132 to avoid endeffects. In an alternate embodiment also shown in FIG. 5 for simplicity,a stationary irradiance sensor 108 b can be located at or near theexposure bed 25, typically near or at a perimeter of the exposure bed,so as not to be disturbed by placement of the precursor on the bed 25 orthe seal 53. Sensors that are suitable for measuring irradiance in someembodiments of the exposure apparatus are UV-A Sensor Models 16163 and16164 available from ATE-Consys GmbH (Bunde, Germany). These aresuitable for both the stationary and the scanning irradiance sensors,70, 108 a, 108 b.

One embodiment of the exposure apparatus 10 shown in FIGS. 7A and 7Bincludes another irradiance sensor 70 that can be moved from one to twoor more positions along a passage 71 that is adjacent to and near thebackside of the exposure bed 25 by a transport assembly 72. Since thepassage 71 is orthogonal to the parallel orientation of the bank oflamps 132, the transport assembly 72 moves the scanning irradiancesensor 70 along the passage 71 and opposite or substantially oppositeeach lamp 32 of the plurality of lamps 132 to measure the intensity orirradiance emitting by each lamp.

The irradiance sensor transport assembly 72 includes an arm member 140having one end 141 that elevates and supports the irradiance sensor 70and a second end 142 connected for rotation on a platform 144. Mountedto the platform 144 is a motor 145 that is coupled to the arm end 142for rotating the arm 140 from a home position Ph that is aligned withthe passage 71 to a scanning position Ps that is oriented about 90degrees from the passage 71 and substantially aligned to the length ofone of the lamps 32 of the plurality of lamps 132. As shown in FIG. 3Band FIG. 5, rotation of the arm 140 to the scanning position Ps locatesthe scanning irradiance sensor 70 between the glass plate 110 and thebank of lamps 132 and adjacent to the front side 130 b of one lamp 32 ofthe plurality of lamps 132. The platform 144 includes two couplings (notshown) that each engage with a side of a slotted track (not shown) thatis attached to an underside of a support 147 for the exposure bed 25,and that is adjacent and parallel to the passage 71. The transportassembly 72 includes a transport motor 149 that is mounted at or near anend of the passage 71 opposite the home station Sh of the sensor 70. Theplatform 144 is coupled to a drive belt 151 that is connected between asprocket or toothed wheel 153 and a second sprocket wheel (not shown)that is coupled to the transport motor 149. When the motor 149 isactivated, the belt 151 moves about the sprocket wheel 153 and secondsprocket wheel causing the couplings to slide or move along theirrespective tracks and thereby move the platform 144 with the arm 140 andthe irradiance sensor 70 along the passage 71.

In some embodiments of a method of maintaining the irradiance of each ofthe lamps 32 or of calibrating the irradiance emitting from each of thelamps 32, all lamps 32 of the plurality of lamps 132 are energized priorto determining the irradiance of any one lamp. Having all the lamps 132energized, even though the scanning irradiance sensor 70 issubstantially determining the irradiance of the each lamp 32individually, is more representative of the radiation condition that theprecursor 20 experiences during an exposure. So although the scanningirradiance sensor 70 is substantially determining the irradiance of theeach lamp individually, the irradiance from one or more lamps adjacentto the lamp that is being measuring may be detected by the irradiancesensor/s. In another embodiment of a method of maintaining theirradiance of each of the lamps or of calibrating the irradianceemitting from each of the lamps 32, only the lamp 32 that is beingmeasured for irradiance is energized. However, as each lamp 32 should atleast be at its target temperature before determining its respectiveirradiance, it will take considerably long time to complete theirradiance measurement for all lamps of the plurality of lamps 132.

The plurality of light tubes 132 when energized typically generatesheat, which particularly in an enclosed environment interior to theexposure apparatus 10 can influence the temperature of the lamps 32, aswell as the irradiance of the lamps, during exposures. So much heat maybe generated by the lamps 32 that the lamps overheat, and it can becomedifficult to maintain the temperature of the lamps within the desiredtemperature range. It is desirable to maintain the temperature constantfrom lamp to lamp within the plurality of light tubes 132, as well asalong the axial length of each of the lamps, and avoid relatively hot orcool regions in the lamps and from lamp to lamp. It is also desirable tomaintain the irradiance constant or substantially constant from lamp tolamp within the plurality of light tube 132. In most embodiments, duringa single exposure the irradiance of the lamp or lamps 32 will notsignificantly drop off or age but the irradiance can be influenced bythe temperature of the lamp or lamps.

One embodiment of the present exposure apparatus 10 and method of useincludes an air distribution assembly 105 which provides the capabilityto maintain the two or more tubular lamps 32 at a constant orsubstantially constant temperature or within a small range oftemperature during exposure. The air distribution assembly 105 can alsoprovide the capability to maintain the two or more tubular lamps 32 at aconstant or substantially constant irradiance or within a small range ofirradiance during exposure. For example, in one embodiment of thepresent apparatus the uniformity of the irradiance emitted in a range of17 to 20 mW/cm² by the one or more lamps 32 due to air impinging thelamps by the air distribution assembly 105 is about +/−5%. That is, theirradiance emitted by the one or more lamps 32 and impinging theexterior surface 28 of the exposure bed 25 and the precursor 20 thereonwill vary by no more than +/−5%. In addition to the uniformity to theirradiance emitted by each lamp, the air distribution assembly alsoprovides similar uniformity of about +/−5% of the irradiance emitted bythe plurality of lamps 132 at the exposure bed, i.e., from edge-to-edgeof the planar area of the bed, and thus impinging the precursor 20 thatresides on the bed.

The air distribution assembly 105 includes the air chamber 115 and theat least one blower 30. The air chamber 115 that is formed by the sheet112 having the at least one opening 117 aligned to each of the at leasttwo lamps 32 as a bottom of the chamber, the cover 122 as a top of thechamber, and sides or cover panels 16 of the lamp housing assembly 14complete the enclosure of the air chamber. The sheet 112 includes atleast one opening 117 for each lamp 32 of the two or more lamps, whereineach opening is aligned parallel to the length of the tubular lamp, anddirects the air exiting the opening to impinge the backside 130 a of thelamp. In some embodiments the sheet 112 includes one opening 117 foreach lamp 32 of the plurality of lamps 132. In some other embodiments,the sheet 112 includes more than one opening 117 for each lamp 32 of theplurality of lamps 132. In most embodiments, the sheet 112 includes aplurality of openings 117, such as slits, for each lamp 32 of theplurality of lamps 132, wherein the plurality of openings are alignedwith the length of each lamp. The sheet 112 can be made of any materialcapable of withstanding conditions, i.e., heat, radiation, within theexposure apparatus 10. In most embodiments, the sheet 112 is made ofmetal, and in one embodiment is made of aluminium. In some embodiments,the sheet 112 is polished to be reflective and/or includes a reflectivecoating on a surface facing the lamp/s 32.

Optionally, the air chamber 115 includes an air dispersing medium 118that forms a layer adjacent to an interior side of the sheet 112 that isopposite to a side of the sheet facing the plurality of lamps 132. Theair dispersing medium 118 helps to uniformly distribute the air in thechamber 115 to each of the plurality of openings 117 in the sheet 112.In some embodiments, the air dispersing medium 118 is a second sheet(not shown) having a plurality of different sizes of openings, and notaligned with the openings on the sheet 112 forming the bottom of thechamber 115. In another embodiment, the air dispersing medium 118 is anonwoven material. In the embodiment shown in FIG. 4 and FIG. 5, the airdispersing medium 118 is a non-compressed nonwoven material having athickness of about 0.7 to about 3.0 cm. In some embodiments, the layerof air dispersing medium 118 contacts with the interior side of thesheet 112 having the openings 117. In some other embodiments, the layerof air dispersing medium is offset and does not contact the interiorside of the sheet 112.

The at least one blower 30 pressurizes the air in the air chamber 115such that the air is expelled from each of the one or more openings 117in the sheet 112 and exits all the openings at the same or substantiallythe same volumetric rate. In the embodiment shown, the air distributionassembly 105 includes two blowers 30. The blowers 30 each include an airintake duct 160 having an intake port 162 that mates with filters 164 a,164 b located in a back ventilation panel 16 of the upright housing 35.The filters 164 a,164 b filter the air that enters through the duct 160and exits at an outlet 166 into the air chamber 115. The entering air isat room temperature. The at least one blower 30 is mounted to the lamphousing assembly 14 and moves with the lamp housing assembly as it istransported to and from the base housing assembly 12. The air intakeduct 160 mates with a first filter 164 a when the lamp housing assembly14 is in the first location Lh, and mates with a second filter 164 bwhen the lamp housing assembly 12 is in the second location Le. In mostembodiments, the at least one blower 30 is continuously operating,bringing air into the chamber 115 to pressurize the chamber, while atleast the one or more lamps 32 are energized. Since the air chamber 115is pressurized, the air exits the openings 117 in the sheet 112 thatforms the bottom of the chamber at a uniform or substantially uniformvolumetric flow rate and impinges upon the backside 130 a of the lamps32. The blower or blowers 30 will change frequency or current toincrease the air into the air chamber 115 and thus the volumetric flowrate exiting the sheet openings 117 and impinging the backside 130 a ofthe lamps thereby cooling the lamps; and, to decrease the air into theair chamber 115 and thus the volumetric flow rate exiting the sheetopenings 117 and impinging the backside 130 a of the lamps 32 to therebyallow the lamps to warm or heat up. In some other embodiments, one ofthe blowers 30 continuously operates, while the second blower cycles onand off to adjust the volumetric flow rate of the air exiting the sheetopenings 117. In one embodiment of operating the exposure apparatus 10to expose a precursor 20 to actinic radiation, the exposure apparatusincludes the lamp assembly 102 that has two or more lamps 32, i.e., aplurality of lamps 132, the air distribution assembly 105 having the airchamber 115 and two blowers 30, and the temperature sensor 107 for thelamp/s and/or the irradiance sensor 108 a, 108 b for the lamp/s which inone embodiment is the stationary irradiance sensor. The precursor 20 ispositioned on an exposure bed 25. Optionally, exposure bed 25 mayundergo one or more steps to assure that the bed and the precursor 20positioned on the bed are at desired conditions. The following steps mayoccur in any order prior to the start of the exposure of the precursor20: the lamp housing assembly 14 is moved to the exposure location Le;the plurality of lamps 132 of the lamp assembly 102 is energized; andthe blowers 30 in the air distribution assembly 105 are activated.

At the exposure location Le, radiation emitting from the front side 130b of the energized plurality of lamps 132 irradiates the precursor 20.During at least the exposure of the precursor 20, air impinges thebackside 130 a of each of the plurality of lamps 132 at a volumetricrate exiting from the air chamber 115 that is adjacent the backside ofthe plurality lamps. In one embodiment, the volumetric rate of airgenerated from the air chamber 115 of the air distribution assembly 105that impinges the plurality of lamps 132 can be about 1.3 meter³ perminute for minimum cooling of the lamps, to about 10 meter³ per minutefor maximum cooling of the lamps. In an embodiment in which theplurality of lamps 132 includes thirty-four individual lamps, thevolumetric rate of air exiting the opening or plurality of openings 117for one lamp (of the 34) is approximately 1/34th of the volumetric rateof air being generated by the air distribution assembly 105. The airexits the air chamber 115 through the plurality of openings 117 of thesheet 112 that are aligned parallel to the tubular length for each ofthe lamps 32. The activated blowers 30 draw air from the room in topressurize the air chamber 115 which uniformly distributes the airexiting each of the plurality of openings 117. The blowers 30 areadjusted, i.e., frequency, with power or current to change the airpressure in the chamber 115. The volumetric rate of the air impingingthe at least two lamps 32 is controlled by maintaining the temperatureof the lamp/s 32, or the irradiance of the lamp/s 32, or both thetemperature and the irradiance of the lamps, to a target temperatureand/or target irradiance. In most embodiments, the temperature of thelamp 32 is measured with the temperature sensor 107, and the blower/s 30is adjusted to change its frequency, i.e., volume of blown air, whichadjusts the air exiting the air chamber 115 through the one or moreopenings 117 based on the measured temperature relative to the targettemperature. In some other embodiments, the irradiance of the lamps ismeasured with one of the stationary irradiance sensor 108 a,108 b andthe blower/s 30 is adjusted to change its frequency, i.e., volume ofblown air, which adjusts the air exiting the one or more openings 117based on the measured irradiance relative to the target irradiance. Inmost other embodiments, both the temperature and the irradiance of thelamp/s 32 are measured and the blower/s 30 is adjusted.

The simplified process control chart of FIG. 11 shows that thecontroller 56 is connected to the at least one blower 30 (via a motorcontroller, not shown) and to the lamp temperature sensor 107 that sendsa signal of the measured temperature to the controller, and thecontroller reads the signal of the measured temperature and compares themeasured temperature to the desired temperature, and signals the atleast one blower to change its frequency or current and thereby adjustthe volumetric rate of air through each of the slots that impinge the atleast two lamps 32. The controller 56 connected to the at least oneblower 30 (via a motor controller not shown) and to at least one of theirradiance sensors 108 a,108 b, wherein the controller reads the signalof the measured irradiance and compares the measured irradiance to thedesired irradiance, and signals the at least one blower to change itsfrequency or current to thereby adjust the volumetric rate of airimpinging the at least two lamps 32.

In some embodiments, during an exposure of a precursor only thetemperature of one or more lamps is measured and adjustment/s are madeat least to the blower/s to control or maintain the temperature of thelamp or lamps to a target lamp temperature. The present apparatus 10maintains the temperature of the lamp or lamps 32 during exposure byusing room temperature air. The heat generated by the lamp or lamps 32during startup of the apparatus 10 is typically sufficient to warm thelamps to the desired target temperature range prior to starting exposureof the precursor. It is within the skill of one in the art to include aheater in the lamp assembly to quickly preheat the lamps to the targettemperature. In some other embodiments, during an exposure of aprecursor both the temperature and the irradiance of one or more lampsare measured and adjustment/s are made to the blower/s to maintain thetemperature and the irradiance of the lamp or lamps to a targettemperature and a target irradiance.

Since the air chamber 115 is pressurized to provide the desired air flowthrough the openings 117 of the sheet 112, after impinging the pluralityof lamps 132 in some embodiments, the air can escape from the lamphousing, (i.e., a section of lamp housing, that is not the air chamber115, and contains the plurality of lamps and optional glass sheet) andvents to the room. In one embodiment, after impinging the lamps 132 theheated air escapes from the section containing the lamps and is activelyremoved from the exposure apparatus 10 through one or more vents oropenings (not shown) that are located around all or a portion of aperimeter of the exposure bed 25 (and within the perimeter of the safetyswitch bar 52 when the lamp housing assembly is at the exposure positionLe) by one or more tangential fans (not shown) that are located in thebase assembly 12 to exhaust the heated air into the room through gapsbetween the apparatus 10 and the floor. Optionally, the vents oropenings at the perimeter of the exposure bed 25 can be connected to theone or more exhaust fans via one or more ducts in the base assembly 12for the heated air to be expelled into the room. In alternateembodiments after impinging the plurality of lamps 132, the air can beactively removed from the section containing the lamps by one or moreexhaust fans located in the lamp housing assembly 14. In one alternateembodiment (not shown), exhaust tubing can be interspersed between allor some of the plurality of lamps 132 in the plane of the lamps. Theexhaust tubing is connected to the exhaust fan that pulls or collectsthe impinged air that is in the lamp housing section through openings inthe tubing to the exhaust from the exposure apparatus. In anotheralternate embodiment (not shown), exhaust tubing can be located at theperimeter of the interior of the lamp housing section, and is connectedto the exhaust fan that pulls or collects the impinged air that is inthe lamp housing section through openings in the tubing to the exhaustfrom the exposure apparatus.

After the exposure, the precursor was exposed to the radiation emittingfrom the at least one lamp with sufficient irradiance to substantiallycomplete the photochemical reaction/s in the composition layer of theprecursor.

In yet another embodiment, after a period of time in which the one ormore lamps are aging, the irradiance of one or more lamps 32 of the lampassembly 102 is measured and adjustment/s are made at least by theadjustable ballast 120 to control or maintain the irradiance of the lampor lamps 30 to a target irradiance.

Lamps age with use, i.e., the irradiance emitted by a lamp or itsintensity is diminishes as the lamp is used. A particular advantage ofthe present method for calibrating or controlling the irradiance of thelamps that are used to expose the photosensitive precursor 20 to actinicradiation in an embodiment of the exposure apparatus 10 that includesthe lamp assembly 102 having lamps 32 with adjustable ballasts 120 isthat only those lamp or lamps that have aged (accelerated) and no longermeet the irradiance or other conditions needs to be changed at any onetime. This is unlike the prior art exposure apparatuses in which alllamps are changed even though only one or two or a few of the pluralityof lamps have significantly aged.

In most embodiments of the exposure apparatus 10, an integrator (notshown), i.e., a radiation integration system, is used during exposurewhich evaluates the intensity or irradiance of the lamps illuminatingthe exposure bed where the precursor lies and compensates the time of anexposure according to the intensity of the radiation emitted by thelamps. The integrator is suitable to compensate for lamp aging to acertain degree, but either the exposures become too long or isinsufficient to provide desired degree of photochemical reaction in thephotosensitive element.

In one embodiment of operating the exposure apparatus 10 to control theradiation emitting from at least one lamp 32 in the exposure apparatusfor exposing the precursor to actinic radiation, the exposure apparatusincludes the lamp assembly 102 that has two or more lamps 32, i.e., aplurality of lamps 132, and an adjustable ballast 120 connected to eachlamp 32, the air distribution assembly 105 having the air chamber 115and two blowers 30, and the temperature sensor 107 for the lamp/s andthe stationary irradiance sensors 108 a 108 b for the lamp/s and thescanning irradiance sensor 70. In the exposure apparatus 10 for exposingthe photosensitive element or precursor 20 to actinic radiation, themethod for controlling the irradiance of at least one lamp 32 having theadjustable ballast 120 may also be referred to herein as a calibrationmethod. The following steps may occur in any order prior to the start ofthe exposure: the lamp housing assembly 14 is moved to the exposurelocation Le; the plurality of lamps 132 of the lamp assembly 102 isenergized; and the blowers 30 in the air distribution assembly 105 areactivated. In most embodiments, the calibration method does not need theprecursor 20 to be exposed, and thus only the exposure bed 25 is exposedto the radiation emitting from the plurality of lamps 132. Thecalibration method for controlling the irradiance of at least one lamp32 having the adjustable ballast 120 is conducted without the precursor20 present and only periodically depending upon use of the system. Inmost embodiments, the calibration method determines the actualirradiance emitting from each lamp 32 of the plurality of lamps 132 and,if necessary, adjusts the irradiance emitting by the lamp to the targetirradiance or in a target irradiance range with the adjustable ballast120.

In most embodiments, the temperature of the lamp/s 32 is measured withthe temperature sensor 107 and the measured lamp temperature is comparedto the target lamp temperature, which in some embodiments is 40 to 45°C. The blowers 30 are activated accordingly as described above tomaintain the temperature of the lamp/s at the target temperature. Withthe lamp housing assembly 14 in the second position Le, the arm member140 of the scanning irradiance sensor 70 is rotated from its homeposition Ph to its scanning position Ps in which arm is align with thelength of the tubular lamp. In the scanning position Ps, the rotation ofthe arm member 140 positions the end 141 with the sensor 70 under thelamp adjacent the front side of a lamp, and above the optional glassplate 110. In the home position Sh for scanning the scanning irradiancesensor 70 aligns or is superposed with the stationary irradiance sensor108 b. The controller 56 compares the measured irradiation from each ofthe scanning and stationary irradiance sensors 70 and 108 b, as anothercheck that the lamps 32 are appropriately ready for calibration.Calibration of one lamp 32 begins with the lamp temperature establishedat the target temperature. The scanning irradiance sensor 70 is moved bythe transport assembly 72 in the passage 71 to orient the sensor 70 inone embodiment opposite or substantially opposite one lamp 32 of theplurality of lamps 132, to measure the irradiance of the lamp. In otherembodiments, the scanning irradiance sensor 70 can be located at otherpositions, i.e., between lamps. Based on comparison of the measuredirradiance to the target irradiance, the power to the one lamp isadjusted by the adjustable ballast 120, thereby adjusting the irradianceemitted from the at least one lamp to match the target irradiance. Thesequence of moving the scanning irradiance sensor 70, measuring theirradiance of the lamp 32 with the scanning sensor 70, and adjusting thepower to the measured lamp with the adjustable ballast 120 to therebyadjust the irradiance emitting from the lamp to a target irradiance isrepeated for most if not all lamps of the plurality of lamps 132 in thelamp assembly 102. In some embodiments, the lamps 32 at the extreme endsof the bank of lamps, i.e., first and last lamps, is not measured andadjusted due to the influence of edge effects. In some embodiments, thelamps at the ends are adjusted based upon the adjustment made by theadjustable ballast 120 for a lamp adjacent to the end lamp.

In one embodiment, the lamps suitable for use have an irradiancecapacity that is about 17 to about 30 mWatts/cm², which when used inconjunction with the adjustable ballasts 120 that adjust the power tothe lamp provides an advantage to significantly extending the lifetimeof the lamp/s before age off, i.e., when the lamps need to be replaceddue to reduced irradiance capacity and/or energy density for suitableexposure times of the photosensitive element. This embodiment of amethod of exposing by maintaining the irradiance of lamp/s using theadjustable ballast provides sufficient uniformity of energy density andirradiance to the precursor for exposure, and which in some cases,allows for only one or a two lamps to be replaced instead of all lamps.The adjustable ballast 120 is used to adjust the power to the lamp 32and thereby adjust the irradiance emitted by the lamp, so that theirradiance emitted by the lamp can be kept uniform or substantiallyuniform over extended periods of time that includes many exposures ofmany precursors. A lamp 32 that is newly installed in the exposureapparatus 10 connects to the adjustable ballast 120 which is adjusted toso that the lamp has target irradiance of, for example, 20 mWatts/cm²;and the adjustable ballast was adjusted, for example, to about 80% ofthe maximum power, i.e., about 20% of the power is used to maintain thetarget irradiance. As the lamp 32 ages, the measured irradiance (by thescanning sensor 70) has decreased from the targeted irradiance, and theadjustable ballast is adjusted, for example, to about 60% of maximumpower, i.e., about 40% of the power is used to return the irradianceemitted by the lamp to the targeted irradiance. Since the adjustableballast 120 can be adjusted to provide from about 5 to 100% of themaximum power from the power source to the lamp 32 or group of two,three, or four lamps.

Photosensitive Element

The photosensitive element is a printing precursor 20 capable ofundergoing exposure to actinic radiation and treating, to form a surfacesuitable for printing. The photosensitive element is used for preparingrelief printing forms and comprises at least one photopolymerizablelayer. Relief printing forms encompass flexographic printing forms andletterpress printing forms. Relief printing is a method of printing inwhich the printing form prints from an image area, where the image areaof the printing form is raised and the non-image area is depressed. Insome other embodiments, the printing form resulting from thephotosensitive element can be suitable for use in gravure orgravure-like printing applications. Gravure printing is a method ofprinting in which the printing form prints from an image area, where theimage area is depressed and consists of small recessed cups or wells tocontain the ink or printing material, and the non-image area is thesurface of the form. Gravure-like printing is similar to gravureprinting except that a relief printing form is used wherein the imagearea is depressed and consists of recessed areas forming wells to carrythe ink which transfer during printing. Optionally, the photosensitiveelement includes a support. Optionally, the photosensitive elementincludes a layer of an actinic radiation opaque material adjacent thephotopolymerizable layer. In one embodiment, the photosensitive elementincludes a layer of photopolymerizable composition composed at least ofa binder, at least one ethylenically unsaturated compound, and aphotoinitiator. In another embodiment, the layer of thephotopolymerizable composition includes an elastomeric binder, at leastone ethylenically unsaturated compound, and a photoinitiator. In someembodiments, the relief printing form is an elastomeric printing form(i.e., the photopolymerizable layer is an elastomeric layer) toaccommodate the compression necessary for contact printing.

Unless otherwise indicated, the term “relief printing plate or element”encompasses plates or elements in any form suitable for flexographicprinting and for letterpress printing. Unless otherwise indicated, theterms “photosensitive element” and “printing form” encompass elements orstructures in any form suitable as precursors for printing, including,but not limited to, flat sheets, plates, seamless continuous forms,cylindrical forms, plates-on-sleeves, and plates-on-carriers.

The support can be any flexible material that is conventionally usedwith photosensitive elements used to prepare relief printing plates. Insome embodiments the support is transparent to actinic radiation toaccommodate “backflash” exposure through the support. Examples ofsuitable support materials include polymeric films such those formed byaddition polymers and linear condensation polymers, transparent foamsand fabrics. Under certain end-use conditions, metals such as aluminum,may also be used as a support, even though a metal support is nottransparent to radiation. A preferred support is a polyester film;particularly preferred is polyethylene terephthalate. The support may bein sheet form or in cylindrical form, such as a sleeve. The sleeve maybe formed from single layer or multiple layers of flexible material.Flexible sleeves made of polymeric films are suitable, as they typicallyare transparent to ultraviolet radiation and thereby accommodatebackflash exposure for building a floor in the cylindrical printingelement. The sleeve may also be made of non-transparent, actinicradiation blocking materials, such as nickel or glass epoxy. The supporthas a thickness typically from 0.002 to 0.250 inch (0.0051 to 0.635 cm).In some embodiments, the thickness for the sheet form is 0.003 to 0.016inch (0.0076 to 0.040 cm). In some embodiments, the sleeve has a wallthickness from 4 to 80 mils (0.010 to 0.203 cm) or more.

Optionally, the element includes an adhesive layer between the supportand the photopolymerizable layer, or a surface of the support that isadjacent the photopolymerizable layer has an adhesion promoting surface.The adhesive layer on the surface of the support can be a subbing layerof an adhesive material or primer or an anchor layer as disclosed inU.S. Pat. No. 2,760,863 and U.S. Pat. No. 3,036,913 to give suitableadhesion between the support and the photopolymerizable layer.Alternatively, the surface of the support on which thephotopolymerizable layer resides can be treated to promote adhesionbetween the support and the photopolymerizable layer, withflame-treatment or electron-treatment, e.g., corona-treated

The photosensitive element includes at least one layer of aphotopolymerizable composition. As used herein, the term“photopolymerizable” is intended to encompass systems that arephotopolymerizable, photocrosslinkable, or both. The photopolymerizablelayer is a solid layer formed of the composition comprising a binder, atleast one ethylenically unsaturated compound, and a photoinitiator. Thephotoinitiator has sensitivity to actinic radiation. Throughout thisspecification actinic light will include ultraviolet radiation and/orvisible light. The solid layer of the photopolymerizable composition istreated with one or more solutions and/or heat to form a relief suitablefor relief printing. As used herein, the term “solid” refers to thephysical state of the layer which has a definite volume and shape andresists forces that tend to alter its volume or shape. A solid layer ofthe photopolymerizable composition may be polymerized (photohardened),or unpolymerized, or both. In some embodiments, the layer of thephotopolymerizable composition is elastomeric.

The binder is not limited and can be a single polymer or mixture ofpolymers. In some embodiments, the binder is an elastomeric binder. Inother embodiments, the binder becomes elastomeric upon exposure toactinic radiation. In some embodiments, the binder is an elastomericblock copolymer of an A-B-A type block copolymer, where A represents anon-elastomeric block, and B represents an elastomeric block. Thenon-elastomeric block A can be a vinyl polymer, such as for example,polystyrene. Examples of the elastomeric block B include polybutadieneand polyisoprene. In some embodiments, the elastomeric binders includepoly(styrene/isoprene/styrene) block copolymers,poly(styrene/butadiene/styrene) block copolymers, and mixtures orcombinations thereof. It is preferred that the binder be present in anamount of at least 50% by weight of the photosensitive composition.

The photopolymerizable composition contains at least one compoundcapable of addition polymerization that is compatible with the binder tothe extent that a clear, non-cloudy photosensitive layer is produced.The at least one compound capable of addition polymerization may also bereferred to as a monomer and can be a single monomer or mixture ofmonomers. Monomers that can be used in the photopolymerizablecomposition are well known in the art and include, but are not limitedto, addition-polymerization ethylenically unsaturated compounds with atleast one terminal ethylenic group. Monomers can be appropriatelyselected by one skilled in the art to provide the photopolymerizablecomposition with suitable properties. The compound capable of additionpolymerization (monomer) is present in at least an amount of 5% byweight of the elastomeric composition.

The photoinitiator can be any single compound or combination ofcompounds which is sensitive to actinic radiation, generating freeradicals which initiate the polymerization of the monomer or monomerswithout excessive termination. Any of the known classes ofphotoinitiators may be used. Alternatively, the photoinitiator may be amixture of compounds, one of which provides the free radicals whencaused to do so by a sensitizer activated by radiation. Preferably, theinitiator is sensitive to visible or ultraviolet radiation.Photoinitiators are generally present in amounts from 0.001% to 10.0%based on the weight of the photopolymerizable composition.

The photopolymerizable layer can contain other additives depending onthe final properties desired. Additional additives to thephotopolymerizable layer include spectral sensitizing agents,sensitizers, plasticizers, rheology modifiers, thermal polymerizationinhibitors, colorants, processing aids, antioxidants, antiozonants, UVabsorber and fillers. The additives should be compatible with the binderand monomer/s.

The thickness of the photopolymerizable layer can vary over a wide rangedepending upon the type of printing form desired, for example, fromabout 0.010 inches to about 0.250 inches or greater (about 0.025 cm toabout 0.64 cm or greater). In some embodiments, the photopolymerizationlayer can range from about 0.002 to about 0.067 inch (about 0.005 cm toabout 0.17 cm) in thickness.

One or more additional layers may be present on top of thephotopolymerizable layer, that is, on a side of the photopolymerizablelayer opposite the support. Depending on desired use, the additionallayers may be opaque or transparent to actinic radiation. They may haveone or more functions for the photosensitive element including, but notlimited to, an elastomeric layer, a release layer, an actinic radiationopaque layer, a barrier layer, an adhesion modifying layer, and a layerwhich alters the surface characteristics of the photosensitive element.The additional layer may comprise at least one thermally removable layeron the photopolymerizable layer, such as disclosed by Fan et al. in U.S.Pat. No. 6,773,859 B2. Other suitable layers include those disclosed aselastomeric layers in the multilayer cover element described in U.S.Pat. No. 4,427,759 and U.S. Pat. No. 4,460,675. The photosensitiveelement can include a wax layer, and/or a barrier layer between anactinic radiation opaque layer and the photopolymerizable layer, orbetween the actinic radiation opaque layer and the elastomeric layer ifpresent. The photosensitive element optionally includes a temporarycover sheet on top of the outermost layer of the photosensitive element.

In one embodiment the precursor includes an actinic radiation opaquelayer on or adjacent the photopolymerizable layer or on top of theelastomeric layer if present. The actinic radiation opaque layer canform an integrated photomask, or in-situ mask, on the precursor, i.e.,photosensitive element, by a digital method of mask formation. Theactinic radiation opaque layer may also be referred to as an infrared(IR)-sensitive layer since the layer may have sensitivity to infraredlaser radiation, and be capable of blocking actinic radiation. In mostembodiments, IR-sensitive layer is opaque to actinic radiation that is,has an optical density greater than or equal to 2.5; can be imaged,preferably by ablating, with an infrared laser. The IR sensitive layercontains material having high absorption in the wavelength (infraredrange between 750 and 20,000 nm. In most embodiments, inorganicpigments, such as, for example, carbon black, graphite, etc. is used toabsorb the IR radiation. The quantity of infrared absorbing material isusually 0.1-40% by weight, relative to the total weight of the layer. Toachieve the optical density of greater than or equal to 2.5 to blockactinic radiation, the infrared-sensitive layer contains a material thatprevents the transmission of actinic radiation. This actinic radiationblocking material can be the same or different than the infraredabsorbing material, and can be, for example, dyes or pigments, and inparticular the aforesaid inorganic pigments. The quantity of thismaterial is usually 1-70% by weight relative to the total weight of thelayer. The infrared-sensitive layer optionally includes a polymericbinder. Other auxiliary agents, such as plasticizers, coating aids, etc.are possible. In one embodiment, the infrared-sensitive layer may becoated or applied to an exterior surface of the photopolymerizable layerof the precursor. The thickness of the infrared-sensitive layer isusually 2 nm to 50 μm, preferably 4 nm to 40 μm. Theseinfrared-sensitive layers and their preparation are described in detail,for example in WO 94/03838 and WO 94/3839.

In an alternate embodiment of digital method of mask formation, thephotosensitive element will not initially include an infrared sensitivelayer. In this case the infrared sensitive layer is the same as orsubstantially the same as the infrared sensitive layer included with thephotosensitive layer as described above. A separate element bearing theinfrared sensitive layer will form an assemblage with the photosensitiveelement such that the infrared sensitive layer is adjacent the surfaceof the photosensitive element opposite the support, which is typicallythe is photopolymerizable layer. The separate element may include one ormore other layers, such as ejection layers or heating layers, to aid inthe digital exposure process. The assemblage is exposed imagewise withinfrared laser radiation to selectively transfer the infrared sensitivelayer and form the image on or disposed above the photopolymerizablelayer as disclosed by Fan et al. in U.S. Pat. No. 5,607,814; andBlanchett in U.S. Pat. Nos. 5,766,819; 5,840,463; and EP 0 891 877 A.Only the portions of the infrared sensitive layer which were transferredwill reside on the photosensitive element forming the in situ mask.

In another embodiment, the photomask image may be created on a separatecarrier and then transferred by application of heat and/or pressure tothe surface of the photopolymerizable layer opposite the support. Thephotopolymerizable layer is typically tacky and will retain thetransferred image. The separate carrier can then be removed from theelement prior to the pre-exposure and/or the imagewise exposure. Theseparate carrier may have an infrared sensitive layer that is imagewiseexposed to laser radiation to selectively remove the material and formthe image. An example of this type of carrier is LaserMask® imaging filmby Rexam, Inc.

In yet another embodiment, digital mask formation can be accomplished byimagewise application of the radiation opaque material in the form ofinkjet inks. Imagewise application of an ink-jet ink can be directly onthe photopolymerizable layer or disposed above the photopolymerizablelayer of the photosensitive element.

In yet another embodiment, a digital mask can be formed in a thermalimaging layer of a separate film, which is then laminated to theelement, prior to imagewise exposure of the photosensitive elementthrough the laminated mask as disclosed by Zwadlo, in U.S. Pat. No.7,279,254. In another embodiment, a digital mask can be formed in-situon the photosensitive element as described above, and a barrier membraneis laminated to the situ mask and the photosensitive layer, prior toimagewise exposure of the photosensitive element through the barriermembrane and in situ mask as disclosed in U.S. Pat. No. 8,158,331.

Regardless of the embodiment by which the mask is created for thephotosensitive element, the mask will include opaque areas and “clear”or transparent areas, which represent a pattern of graphic informationsuitable for printing. The opaque areas of the mask prevent thephotopolymerizable material beneath from being exposed to the radiationand hence those areas of the photopolymerizable layer covered by thedark areas do not polymerize, i.e., uncured portions of the layer. The“clear” areas of the mask expose the photopolymerizable layer to actinicradiation and polymerize or crosslink, i.e., cured portions of thelayer.

Imagewise exposure is carried out by exposing the photosensitive elementthrough an image-bearing photomask using at least one embodiment of thepresent exposure apparatus and method. In most embodiments, thephotomask is integrated with the precursor as described above. In mostembodiments the integrated photomask is formed on the precursor (i.e.,photosensitive element) by a digital method in which the precursor isimagewise exposed to infrared laser radiation to form an integratedphotomask on the precursor, prior to exposure to actinic radiation bythe present exposure apparatus. The integrated photomask may also bereferred to as an in-situ mask. The infrared laser exposure can becarried out using various types of infrared lasers, which emit in therange 750 to 20,000 nm. Infrared lasers including, diode lasers emittingin the range 780 to 2,000 nm and Nd:YAG lasers emitting at 1064 nm arepreferred. A suitable infrared laser exposure apparatus is disclosed byFan et al. in U.S. Pat. Nos. 5,654,125 and 5,760,880. In so-calleddigital imaging, the radiation opaque layer is exposed imagewise toinfrared laser radiation to form the image on or disposed above thephotopolymerizable layer, i.e., the in-situ mask. The infrared laserradiation can selectively remove, e.g., ablate or vaporize, the infraredsensitive layer (i.e., radiation opaque layer) from thephotopolymerizable layer, as disclosed by Fan in U.S. Pat. No.5,262,275; U.S. Pat. No. 5,719,009; and U.S. Pat. No. 6,238,837. Theintegrated photomask remains on the photosensitive element forsubsequent step of exposure to actinic radiation by the present exposureapparatus. The infrared laser radiation can selectively transfer theinfrared sensitive layer to the photopolymerizable layer as describedabove.

One or more embodiments of the present exposure apparatus and method canalso be used for an overall back exposure. An overall or blanketexposure of the precursor through the support, i.e., back of precursor,may be conducted to polymerize a predetermined thickness of thephotopolymer layer adjacent the support. This polymerized portion of thephotopolymer layer is often designated a floor. The floor providesimproved adhesion between the photopolymerizable layer and the support,helps highlight dot resolution and also establishes the depth of theplate relief. The floor thickness varies with the time of exposure,exposure source, etc. All radiation sources suitable for imagewise mainexposure may be used. The exposure is generally for 1-30 minutes. Insome embodiments, the overall back exposure is conducted during themanufacture of the (uncured) precursor, and thus simplifies the stepsnecessary for a customer to convert the precursor to a printing formhaving a relief surface. In other embodiments, the overall back exposuremay be conducted before or after imagewise exposure by a customer.

The precursor is imagewise exposed or blanket exposed, i.e., overallexposed, to actinic radiation in the present exposure apparatus. Theprecursor is exposed by mounting the precursor on the exposure bed,positioning the plurality of tubular lamps adjacent and in relativelyclose proximity to the precursor, and energizing the tubular lamps toemit the actinic radiation. Upon imagewise exposure, theradiation-exposed areas of the photopolymerizable layer are converted tothe insoluble state with no significant polymerization or crosslinkingtaking place in the unexposed areas of the layer.

After the treatment step, the precursor can be uniformly post-exposedand light finished by the present exposure apparatus to ensure that thephotopolymerization process is complete and that the so formed printingform will remain stable during printing and storage. This post-exposurestep can utilize the same radiation source as the imagewise mainexposure. Furthermore, if the surface of the precursor, i.e., print formwith the relief surface, is still tacky, detackification treatments maybe applied. Such methods, which are also called “finishing”, are wellknown in the art. For example, tackiness can be eliminated by atreatment of the print form with bromine or chlorine solutions.Preferably, detackification is accomplished by exposure to UV radiationsources having a wavelength not longer than 300 nm. This so-called“light-finishing” is disclosed in European Published Patent Application0 017927 and U.S. Pat. No. 4,806,506. Various finishing methods may alsobe combined. In some embodiments, the post-exposure and the finishingexposure are done at the same time on the precursor 20 using the presentexposure apparatus 10 that has both sources of radiation, which in theembodiment shown is located in drawer 13 a, and the precursor is placedin drawer 13 b.

Following imagewise exposure to actinic radiation through the mask, theprecursor is treated to remove unpolymerized areas in thephotopolymerizable layer and thereby form a relief image. The treatingstep removes at least the photopolymerizable layer in the areas thatwere not exposed to actinic radiation, i.e., the unexposed areas oruncured areas, of the photopolymerizable layer. Except for theelastomeric capping layer, typically the additional layers that may bepresent on the photopolymerizable layer are removed or substantiallyremoved from the polymerised areas of the photopolymerizable layer. Forprecursors including an IR-sensitive layer for digital formation of themask, the treating step that forms the relief image in thephotopolymerizable layer may also remove the mask image (which had beenexposed to actinic radiation).

Treating of the photosensitive element includes (1) “wet” developmentwherein the precursor is contacted with a suitable developer solution towashout unpolymerized areas and/or (2) “dry” development wherein theprecursor is heated to a development temperature which causes theunpolymerized areas of the photopolymerizable layer to melt or soften orflow and then are removed. Dry development may also be called thermaldevelopment. It is also contemplated that combinations of wet and drytreatment can be used to form the relief.

Wet development can be carried out at room temperature but usually iscarried out at about 80 to 100° F. The developers can be organicsolvents, aqueous or semi-aqueous solutions, and water. The choice ofthe developer will depend primarily on the chemical nature of thephotopolymerizable material to be removed. It is well within the skillof a person in the art to select a suitable solvent developer.Development time can vary based on the thickness and type of thephotopolymerizable material, the solvent being used, and the equipmentand its operating temperature. Developer can be applied in anyconvenient manner, including immersion, spraying and brush or rollerapplication. Washout can be carried out in an automatic processing unitwhich uses a developer and optionally mechanical brushing action toremove the uncured portions of the plate, leaving a relief constitutingthe exposed image and the floor. Following treatment by developing insolution, the treated precursors are generally blotted or wiped dry, andthen more fully dried in a forced air or infrared oven. Drying times andtemperatures may vary based on equipment design, air flow, andmaterials.

Treating the precursor thermally includes heating the photosensitiveelement to a temperature sufficient to cause the uncured portions of thephotopolymerizable layer to liquefy, i.e., soften or melt or flow, andremoving the uncured portions. The layer of the photosensitivecomposition is capable of partially liquefying upon thermal development.That is, during thermal development the uncured composition must softenor melt at a reasonable processing or developing temperature. If theprecursor includes one or more additional layers on thephotopolymerizable layer, it is desirable (but not necessary) that theone or more additional layers are also removable in the range ofacceptable developing temperatures for the photopolymerizable layer. Thepolymerized areas (cured portions) of the photopolymerizable layer havea higher melting temperature than the unpolymerized areas (uncuredportions) and therefore do not melt, soften, or flow at the thermaldevelopment temperatures. The uncured portions can be removed from thecured portions of the composition layer by any means including air orliquid stream under pressure as described in U.S. publication2004/0048199 A1, vacuum as described in Japanese publication 53-008655,and contacting with an absorbent material as described in U.S. Pat. No.3,060,023; U.S. Pat. No. 3,264,103; U.S. Pat. No. 5,015,556; U.S. Pat.No. 5,175,072; U.S. Pat. No. 5,215,859; U.S. Pat. No. 5,279,697; andU.S. Pat. No. 6,797,454. A preferred method for removing the uncuredportions is by contacting an outermost surface of the element to anabsorbent surface, such as a development medium, to absorb or wick awayor blot the melt portions.

The term “melt” is used to describe the behavior of the unirradiated(uncured) portions of the composition layer subjected to an elevatedtemperature that softens and reduces the viscosity to permit absorptionby the absorbent material. However throughout this specification theterms “melting”, “softening”, and “liquefying” may be used to describethe behavior of the heated unirradiated portions of the compositionlayer, regardless of whether the composition may or may not have a sharptransition temperature between a solid and a liquid state. A widetemperature range may be utilized to “melt” the composition layer forthe purposes of this invention. Absorption may be slower at lowertemperatures and faster at higher temperatures during successfuloperation of the process.

The thermal treating steps of heating the photosensitive element andcontacting an outermost surface of the element with development mediumcan be done at the same time, or in sequence provided that the uncuredportions of the photopolymerizable layer are still soft or in a meltstate when contacted with the development medium. The at least onephotopolymerizable layer (and the additional layer/s) are heated byconduction, convection, radiation, or other heating methods to atemperature sufficient to effect melting of the uncured portions but notso high as to effect distortion of the cured portions of the layer. Theone or more additional layers disposed above the photopolymerizablelayer may soften or melt or flow and be absorbed as well by thedevelopment medium. The photosensitive element is heated to a surfacetemperature above about 40° C., preferably from about 40° C. to about230° C. (104-446° F.) in order to effect melting or flowing of theuncured portions of the photopolymerizable layer. By maintaining more orless intimate contact of the development medium with thephotopolymerizable layer that is molten in the uncured regions, atransfer of the uncured photosensitive material from thephotopolymerizable layer to the development medium takes place. Whilestill in the heated condition, the development medium is separated fromthe cured photopolymerizable layer in contact with the support layer toreveal the relief structure. A cycle of the steps of heating thephotopolymerizable layer and contacting the molten (portions) layer withthe development medium can be repeated as many times as necessary toadequately remove the uncured material and create sufficient reliefdepth.

Apparatuses suitable for thermally developing the photosensitive elementare disclosed by Peterson et al. in U.S. Pat. No. 5,279,697, and also byJohnson et al. in U.S. Pat. No. 6,797,454. The photosensitive elementmay be placed on a drum or a planar surface in order for thermaltreatment to be carried out.

The development medium is selected to have a melt temperature exceedingthe melt or softening or liquefying temperature of the unirradiated oruncured portions of the radiation curable composition and having goodtear resistance at the same operating temperatures. The developmentmedium is selected from non-woven materials, paper stocks, fibrous wovenmaterial, open-celled foam materials, porous materials that contain moreor less a substantial fraction of their included volume as void volume.The development medium should also possess a high absorbency for themolten elastomeric composition.

What is claimed is:
 1. An exposure apparatus for exposing aphotosensitive element to actinic radiation comprising: an exposure bedhaving a first side and a second side opposite the first side, the firstside of the bed has an exterior surface for supporting thephotosensitive element, the exterior surface having at least one orificethat is connected to a means for removing air between the photosensitiveelement and the exterior surface; an assembly for controllingtemperature of the bed to allow for heating and cooling that is adjacentthe second side of the bed comprising at least one coil having fluidtransported therein, and a means for adjusting temperature of the fluid;and, is a lamp assembly disposed above the bed comprising at least onelamp positioned to irradiate the photosensitive element supported on theexterior surface with the actinic radiation.
 2. The exposure apparatusof claim 1 wherein the bed comprises two or more orifices that arecentrally located on the exterior surface of the bed and are covered bythe photosensitive element supported on the bed, wherein the means forremoving air provides uniform contact of a backside of thephotosensitive element with the exterior surface of the bed.
 3. Theexposure apparatus of claim 1 wherein the bed comprises two or moreorifices and the exterior surface further comprises at least one channelconnecting two or more of the orifices.
 4. The exposure apparatus ofclaim 1 wherein the bed comprises two or more orifices and the exteriorsurface further comprises two or more channels that are connecteddirectly or indirectly to two or more of the orifices.
 5. The exposureapparatus of claim 1 wherein the at least one orifice forms a passagefrom the first side to the second side, wherein the passage connects toa vacuum pump as the means for removing air.
 6. The exposure apparatusof claim 1 wherein the exterior surface is textured.
 7. The exposureapparatus of claim 1 wherein the bed is made of metal.
 8. The exposureapparatus of claim 1 wherein the exterior surface of the bed is planar.9. The exposure apparatus of claim 1 wherein the means for removing airis a vacuum pump.
 10. The exposure apparatus of claim 1 wherein themeans for changing the temperature of the fluid comprises a heater toheat the fluid, a chiller to cool the fluid, wherein the heater and thechiller are connected by at least one conduit to the fluid in the coil,and at least one pump to transport the fluid through the coil and the atleast one conduit through the heater or the chiller.
 11. The exposureapparatus of claim 10 wherein the assembly further comprises a reservoirfor the fluid that is connected to the coil and to the at least oneconduit, and a recirculating conduit connecting the reservoir and thecoil wherein the at least one pump transports the fluid from thereservoir through the conduit to the heater or to the chiller or throughthe recirculating conduit to the coil.
 12. The exposure apparatus ofclaim 10 further comprising a sensor disposed on or adjacent the secondside of the bed for determining the temperature of the bed, and acontroller connected to the sensor and the temperature-controllingassembly that directs the fluid to the at least one conduit through theheater or the chiller to respectively heat the fluid or cool the fluidas the fluid transports to the at least one coil, and thereby adjustingthe temperature of the bed to a target temperature.
 13. A method forexposing a photosensitive element to actinic radiation comprising:supporting the photosensitive element on an exterior surface of a firstside of an exposure bed wherein the bed has a second side opposite thefirst side and at least one orifice from the exterior surface; removingair between the photosensitive element and the exterior surface throughthe at least one orifice; determining a temperature of the bed;controlling the temperature of the bed to a target temperature bytransporting a fluid through at least one coil adjacent the second sideof the bed; and, adjusting a temperature of the fluid by heating thefluid and cooling the fluid.
 14. The method of claim 13 furthercomprising exposing the photosensitive element to the actinic radiation.15. The method of claim 13 wherein the removing air step comprisespulling a vacuum with a vacuum pump connecting to an end of a passage tothe at least one orifice.
 16. The method of claim 13 further comprisingtransporting the fluid through a reservoir connecting to a heater forheating the fluid and a chiller for chilling the fluid; and transportingthe fluid through the heater or the chiller to the at least one coil toraise or lower respectively the temperature of the bed to the targettemperature for the bed.
 17. The method of claim 13 further comprisingtransporting the fluid through a reservoir connecting to a heater forheating the fluid, a chiller for chilling the fluid, and a recirculatingconduit for recirculating fluid through the reservoir and the at leastone coil; and transporting the fluid through a) the heater or thechiller to the at least one coil to raise or lower respectively thetemperature of the bed to the target temperature for the bed, or b) therecirculating conduit to maintain the temperature of the bed to thetarget temperature.
 18. The method of claim 13 further comprisingexposing the photosensitive element to the actinic radiation, whereinprior to or at the beginning of the exposing the fluid is heated to warmthe temperature of bed to the target temperature, and during exposingthe fluid is cooled to cool the temperature of the bed to the targettemperature.
 19. A method for preparing a relief printing form from aphotosensitive element having a layer of a photopolymerizablecomposition comprising: imagewise exposing the photosensitive elementthrough a mask to actinic radiation according to the method of claim 13,forming at least a cured portion and at least a uncured portion of thelayer; and, treating the exposed element to remove the uncured portionsthereby forming a relief structure suitable for printing.